Tag Archives: edmundchattoebrown

Reply to Frank Dignum

By Edmund Chattoe-Brown

This is a reply to Frank Dignum’s reply (about Edmund Chattoe-Brown’s review of Frank’s book)

As my academic career continues, I have become more and more interested in the way that people justify their modelling choices, for example, almost every Agent-Based Modeller makes approving noises about validation (in the sense of comparing real and simulated data) but only a handful actually try to do it (Chattoe-Brown 2020). Thus I think two specific statements that Frank makes in his response should be considered carefully:

  1. … we do not claim that we have the best or only way of developing an Agent-Based Model (ABM) for crises.” Firstly, negative claims (“This is not a banana”) are not generally helpful in argument. Secondly, readers want to know (or should want to know) what is being claimed and, importantly, how they would decide if it is true “objectively”. Given how many models sprang up under COVID it is clear that what is described here cannot be the only way to do it but the question is how do we know you did it “better?” This was also my point about institutionalisation. For me, the big lesson from COVID was how much the automatic response of the ABM community seems to be to go in all directions and build yet more models in a tearing hurry rather than synthesise them, challenge them or test them empirically. I foresee a problem both with this response and our possible unwillingness to be self-aware about it. Governments will not want a million “interesting” models to choose from but one where they have externally checkable reasons to trust it and that involves us changing our mindset (to be more like climate modellers for example, Bithell & Edmonds 2020). For example, colleagues and I developed a comparison methodology that allowed for the practical difficulties of direct replication (Chattoe-Brown et al. 2021).
  2. The second quotation which amplifies this point is: “But we do think it is an extensive foundation from which others can start, either picking up some bits and pieces, deviating from it in specific ways or extending it in specific ways.” Again, here one has to ask the right question for progress in modelling. On what scientific grounds should people do this? On what grounds should someone reuse this model rather than start their own? Why isn’t the Dignum et al. model built on another “market leader” to set a good example? (My point about programming languages was purely practical not scientific. Frank is right that the model is no less valid because the programming language was changed but a version that is now unsupported seems less useful as a basis for the kind of further development advocated here.)

I am not totally sure I have understood Frank’s point about data so I don’t want to press it but my concern was that, generally, the book did not seem to “tap into” relevant empirical research (and this is a wider problem that models mostly talk about other models). It is true that parameter values can be adjusted arbitrarily in sensitivity analysis but that does not get us any closer to empirically justified parameter values (which would then allow us to attempt validation by the “generative methodology”). Surely it is better to build a model that says something about the data that exists (however imperfect or approximate) than to rely on future data collection or educated guesses. I don’t really have the space to enumerate the times the book said “we did this for simplicity”, “we assumed that” etc. but the cumulative effect is quite noticeable. Again, we need to be aware of the models which use real data in whatever aspects and “take forward” those inputs so they become modelling standards. This has to be a collective and not an individualistic enterprise.

References

Bithell, M. and Edmonds, B. (2020) The Systematic Comparison of Agent-Based Policy Models – It’s time we got our act together!. Review of Artificial Societies and Social Simulation, 11th May 2021. https://rofasss.org/2021/05/11/SystComp/

Chattoe-Brown, E. (2020) A Bibliography of ABM Research Explicitly Comparing Real and Simulated Data for Validation. Review of Artificial Societies and Social Simulation, 12th June 2020. https://rofasss.org/2020/06/12/abm-validation-bib/

Chattoe-Brown, E. (2021) A review of “Social Simulation for a Crisis: Results and Lessons from Simulating the COVID-19 Crisis”. Journal of Artificial Society and Social Simulation. 24(4). https://www.jasss.org/24/4/reviews/1.html

Chattoe-Brown, E., Gilbert, N., Robertson, D. A., & Watts, C. J. (2021). Reproduction as a Means of Evaluating Policy Models: A Case Study of a COVID-19 Simulation. medRxiv 2021.01.29.21250743; DOI: https://doi.org/10.1101/2021.01.29.21250743

Dignum, F. (2020) Response to the review of Edmund Chattoe-Brown of the book “Social Simulations for a Crisis”. Review of Artificial Societies and Social Simulation, 4th Nov 2021. https://rofasss.org/2021/11/04/dignum-review-response/

Dignum, F. (Ed.) (2021) Social Simulation for a Crisis: Results and Lessons from Simulating the COVID-19 Crisis. Springer. DOI:10.1007/978-3-030-76397-8


Chattoe-Brown, E. (2021) Reply to Frank Dignum. Review of Artificial Societies and Social Simulation, 10th November 2021. https://rofasss.org/2021/11/10/reply-to-dignum/


 

Response to the review of Edmund Chattoe-Brown of the book “Social Simulations for a Crisis”

By Frank Dignum

This is a reply to a review in JASSS (Chattoe-Brown 2021) of (Dignum 2021).

Before responding to some of the specific concerns of Edmund I would like to thank him for the thorough review. I am especially happy with his conclusion that the book is solid enough to make it a valuable contribution to scientific progress in modelling crises. That was the main aim of the book and it seems that is achieved. I want to reiterate what we already remarked in the book; we do not claim that we have the best or only way of developing an Agent-Based Model (ABM) for crises. Nor do we claim that our simulations were without limitations. But we do think it is an extensive foundation from which others can start, either picking up some bits and pieces, deviating from it in specific ways or extending it in specific ways.

The concerns that are expressed by Edmund are certainly valid. I agree with some of them, but will nuance some others. First of all the concern about the fact that we seem to abandon the NetLogo implementation and move to Repast. This fact does not make the ABM itself any less valid! In itself it is also an important finding. It is not possible to scale such a complex model in NetLogo beyond around two thousand agents. This is not just a limitation of our particular implementation, but a more general limitation of the platform. It leads to the important challenge to get more computer scientists involved to develop platforms for social simulations that both support the modelers adequately and provide efficient and scalable implementations.

That the sheer size of the model and the results make it difficult to trace back the importance and validity of every factor on the results is completely true. We have tried our best to highlight the most important aspects every time. But, this leaves questions as to whether we make the right selection of highlighted aspects. As an illustration to this, we have been busy for two months to justify our results of the simulations of the effectiveness of the track and tracing apps. We basically concluded that we need much better integrated analysis tools in the simulation platform. NetLogo is geared towards creating one simulation scenario, running the simulation and analyzing the results based on a few parameters. This is no longer sufficient when we have a model with which we can create many scenarios and have many parameters that influence a result. We used R now to interpret the flood of data that was produced with every scenario. But, R is not really the most user friendly tool and also not specifically meant for analyzing the data from social simulations.

Let me jump to the third concern of Edmund and link it to the analysis of the results as well. While we tried to justify the results of our simulation on the effectiveness of the track and tracing app we compared our simulation with an epidemiological based model. This is described in chapter 12 of the book. Here we encountered the difference in assumed number of contacts per day a person has with other persons. One can take the results, as quoted by Edmund as well, of 8 or 13 from empirical work and use them in the model. However, the dispute is not about the number of contacts a person has per day, but what counts as a contact! For the COVID-19 simulations standing next to a person in the queue in a supermarket for five minutes can count as a contact, while such a contact is not a meaningful contact in the cited literature. Thus, we see that what we take as empirically validated numbers might not at all be the right ones for our purpose. We have tried to justify all the values of parameters and outcomes in the context for which the simulations were created. We have also done quite some sensitivity analyses, which we did not all report on just to keep the volume of the book to a reasonable size. Although we think we did a proper job in justifying all results, that does not mean that one can have different opinions on the value that some parameters should have. It would be very good to check the influence on the results of changes in these parameters. This would also progress scientific insights in the usefulness of complex models like the one we made!

I really think that an ABM crisis response should be institutional. That does not mean that one institution determines the best ABM, but rather that the ABM that is put forward by that institution is the result of a continuous debate among scientists working on ABM’s for that type of crisis. For us, one of the more important outcomes of the ASSOCC project is that we really need much better tools to support the types of simulations that are needed for a crisis situation. However, it is very difficult to develop these tools as a single group. A lot of the effort needed is not publishable and thus not valued in an academic environment. I really think that the efforts that have been put in platforms such as NetLogo and Repast are laudable. They have been made possible by some generous grants and institutional support. We argue that this continuous support is also needed in order to be well equipped for a next crisis. But we do not argue that an institution would by definition have the last word in which is the best ABM. In an ideal case it would accumulate all academic efforts as is done in the climate models, but even more restricted models would still be better than just having a thousand individuals all claiming to have a useable ABM while governments have to react quickly to a crisis.

The final concern of Edmund is about the empirical scale of our simulations. This is completely true! Given the scale and details of what we can incorporate we can only simulate some phenomena and certainly not everything around the COVID-19 crisis. We tried to be clear about this limitation. We had discussions about the Unity interface concerning this as well. It is in principle not very difficult to show people walking in the street, taking a car or a bus, etc. However, we decided to show a more abstract representation just to make clear that our model is not a complete model of a small town functioning in all aspects. We have very carefully chosen which scenarios we can realistically simulate and give some insights in reality from. Maybe we should also have discussed more explicitly all the scenarios that we did not run with the reasons why they would be difficult or unrealistic in our ABM. One never likes to discuss all the limitations of one’s labor, but it definitely can be very insightful. I have made up for this a little bit by submitting an to a special issue on predictions with ABM in which I explain in more detail, which should be the considerations to use a particular ABM to try to predict some state of affairs. Anyone interested to learn more about this can contact me.

To conclude this response to the review, I again express my gratitude for the good and thorough work done. The concerns that were raised are all very valuable to concern. What I tried to do in this response is to highlight that these concerns should be taken as a call to arms to put effort in social simulation platforms that give better support for creating simulations for a crisis.

References

Dignum, F. (Ed.) (2021) Social Simulation for a Crisis: Results and Lessons from Simulating the COVID-19 Crisis. Springer. DOI:10.1007/978-3-030-76397-8

Chattoe-Brown, E. (2021) A review of “Social Simulation for a Crisis: Results and Lessons from Simulating the COVID-19 Crisis”. Journal of Artificial Society and Social Simulation. 24(4). https://www.jasss.org/24/4/reviews/1.html


Dignum, F. (2020) Response to the review of Edmund Chattoe-Brown of the book “Social Simulations for a Crisis”. Review of Artificial Societies and Social Simulation, 4th Nov 2021. https://rofasss.org/2021/11/04/dignum-review-response/


 

Where Now For Experiments In Agent-Based Modelling? Report of a Round Table at SSC2021, held on 22 September 2021


By Dino Carpentras1, Edmund Chattoe-Brown2*, Bruce Edmonds3, Cesar García-Diaz4, Christian Kammler5, Anna Pagani6 and Nanda Wijermans7

*Corresponding author, 1Centre for Social Issues Research, University of Limerick, 2School of Media, Communication and Sociology, University of Leicester, 3Centre for Policy Modelling, Manchester Metropolitan University, 4Department of Business Administration, Pontificia Universidad Javeriana, 5Department of Computing Science, Umeå University, 6Laboratory on Human-Environment Relations in Urban Systems (HERUS), École Polytechnique Fédérale de Lausanne (EPFL), 7Stockholm Resilience Centre, Stockholm University.

Introduction

This round table was convened to advance and improve the use of experimental methods in Agent-Based Modelling, in the hope that both existing and potential users of the method would be able to identify steps towards this aim[i]. The session began with a presentation by Bruce Edmonds (http://cfpm.org/slides/experiments%20and%20ABM.pptx) whose main argument was that the traditional idea of experimentation (controlling extensively for the environment and manipulating variables) was too simplistic to add much to the understanding of the sort of complex systems modelled by ABMs and that we should therefore aim to enhance experiments (for example using richer experimental settings, richer measures of those settings and richer data – like discussions between participants as well as their behaviour). What follows is a summary of the main ideas discussed organised into themed sections.

What Experiments Are

Defining the field of experiments proved to be challenging on two counts. The first was that there are a number of labels for potentially relevant approaches (experiments themselves – for example, Boero et al. 2010, gaming – for example, Tykhonov et al. 2008, serious games – for example Taillandier et al. 2019, companion/participatory modelling – for example, Ramanath and Gilbert 2004 and web based gaming – for example, Basole et al. 2013) whose actual content overlap is unclear. Is it the case that a gaming approach is generally more in line with the argument proposed by Edmonds? How can we systematically distinguish the experimental content of a serious game approach from a gaming approach? This seems to be a problem in immature fields where the labels are invented first (often on the basis of a few rather divergent instances) and the methodology has to grow into them. It would be ludicrous if we couldn’t be sure whether a piece of research was survey based or interview based (and this would radically devalue the associated labels if it were so.)

The second challenge is also more general in Agent-Based Modelling which is the same labels being used differently by different researchers. It is not productive to argue about which uses are correct but it is important that the concepts behind the different uses are clear so a common scheme of labelling might ultimately be agreed. So, for example, experiment can be used (and different round table participants had different perspectives on the uses they expected) to mean laboratory experiments (simplified settings with human subjects – again see, for example, Boero et al. 2010), experiments with ABMs (formal experimentation with a model that doesn’t necessarily have any empirical content – for example, Doran 1998) and natural experiments (choice of cases in the real world to, for example, test a theory – see Dinesen 2013).

One approach that may help with this diversity is to start developing possible dimensions of experimentation. One might be degree of control (all the way from very stripped down behavioural laboratory experiments to natural situations where the only control is to select the cases). Another might be data diversity: From pure analysis of ABMs (which need not involve data at all), through laboratory experiments that record only behaviour to ethnographic collection and analysis of diverse data in rich experiments (like companion modelling exercises.) But it is important for progress that the field develops robust concepts that allow meaningful distinctions and does not get distracted into pointless arguments about labelling. Furthermore, we must consider the possible scientific implications of experimentation carried out at different points in the dimension space: For example, what are the relative strengths and limitations of experiments that are more or less controlled or more or less data diverse? Is there a “sweet spot” where the benefit of experiments is greatest to Agent-Based Modelling? If so, what is it and why?

The Philosophy of Experiment

The second challenge is the different beliefs (often associated with different disciplines) about the philosophical underpinnings of experiment such as what we might mean by a cause. In an economic experiment, for example, the objective may be to confirm a universal theory of decision making through displayed behaviour only. (It is decisions described by this theory which are presumed to cause the pattern of observed behaviour.) This will probably not allow the researcher to discover that their basic theory is wrong (people are adaptive not rational after all) or not universal (agents have diverse strategies), or that some respondents simply didn’t understand the experiment (deviations caused by these phenomena may be labelled noise relative to the theory being tested but in fact they are not.)

By contrast qualitative sociologists believe that subjective accounts (including accounts of participation in the experiment itself) can be made reliable and that they may offer direct accounts of certain kinds of cause: If I say I did something for a certain reason then it is at least possible that I actually did (and that the reason I did it is therefore its cause). It is no more likely that agreement will be reached on these matters in the context of experiments than it has been elsewhere. But Agent-Based Modelling should keep its reputation for open mindedness by seeing what happens when qualitative data is also collected and not just rejecting that approach out of hand as something that is “not done”. There is no need for Agent-Based Modelling blindly to follow the methodology of any one existing discipline in which experiments are conducted (and these disciplines often disagree vigorously on issues like payment and deception with no evidence on either side which should also make us cautious about their self-evident correctness.)

Finally, there is a further complication in understanding experiments using analogies with the physical sciences. In understanding the evolution of a river system, for example, one can control/intervene, one can base theories on testable micro mechanisms (like percolation) and one can observe. But there is no equivalent to asking the river what it intends (whether we can do this effectively in social science or not).[ii] It is not totally clear how different kinds of data collection like these might relate to each other in the social sciences, for example, data from subjective accounts, behavioural experiments (which may show different things from what respondents claim) and, for example, brain scans (which side step the social altogether.) This relationship between different kinds of data currently seems incompletely explored and conceptualised. (There is a tendency just to look at easy cases like surveys versus interviews.)

The Challenge of Experiments as Practical Research

This is an important area where the actual and potential users of experiments participating in the round table diverged. Potential users wanted clear guidance on the resources, skills and practices involved in doing experimental work (and see similar issues in the behavioural strategy literature, for example, Reypens and Levine 2018). At the most basic level, when does a researcher need to do an experiment (rather than a survey, interviews or observation), what are the resource requirements in terms of time, facilities and money (laboratory experiments are unusual in often needing specific funding to pay respondents rather than substituting the researcher working for free) what design decisions need to be made (paying subjects, online or offline, can subjects be deceived?), how should the data be analysed (how should an ABM be validated against experimental data?) and so on.[iii] (There are also pros and cons to specific bits of potentially supporting technology like Amazon Mechanical Turk, Qualtrics and Prolific, which have not yet been documented and systematically compared for the novice with a background in Agent-Based Modelling.) There is much discussion about these matters in the traditional literatures of social sciences that do experiments (see, for example, Kagel and Roth 1995, Levine and Parkinson 1994 and Zelditch 2014) but this has not been summarised and tuned specifically for the needs of Agent-Based Modellers (or published where they are likely to see it).

However, it should not be forgotten that not all research efforts need this integration within the same project, so thinking about the problems that really need it is critical. Nonetheless, triangulation is indeed necessary within research programmes. For instance, in subfields such as strategic management and organisational design, it is uncommon to see an ABM integrated with an experiment as part of the same project (though there are exceptions, such as Vuculescu 2017). Instead, ABMs are typically used to explore “what if” scenarios, build process theories and illuminate potential empirical studies. In this approach, knowledge is accumulated instead through the triangulation of different methodologies in different projects (see Burton and Obel 2018). Additionally, modelling and experimental efforts are usually led by different specialists – for example, there is a Theoretical Organisational Models Society whose focus is the development of standards for theoretical organisation science.

In a relatively new and small area, all we often have is some examples of good practice (or more contentiously bad practice) of which not everyone is even aware. A preliminary step is thus to see to what extent people know of good practice and are able to agree that it is good (and perhaps why it is good).

Finally, there was a slightly separate discussion about the perspectives of experimental participants themselves. It may be that a general problem with unreal activity is that you know it is unreal (which may lead to problems with ecological validity – Bornstein 1999.) On the other hand, building on the enrichment argument put forward by Edmonds (above), there is at least anecdotal observational evidence that richer and more realistic settings may cause people to get “caught up” and perhaps participate more as they would in reality. Nonetheless, there are practical steps we can take to learn more about these phenomena by augmenting experimental designs. For example we might conduct interviews (or even group discussions) before and after experiments. This could make the initial biases of participants explicit and allow them to self-evaluate retrospectively the extent to which they got engaged (or perhaps even over-engaged) during the game. The first such questionnaire could be available before attending the experiment, whilst another could be administered right after the game (and perhaps even a third a week later). In addition to practical design solutions, there are also relevant existing literatures that experimental researchers should probably draw on in this area, for example that on systemic design and the associated concept of worldviews. But it is fair to say that we do not yet fully understand the issues here but that they clearly matter to the value of experimental data for Agent-Based Modelling.[iv]

Design of Experiments

Something that came across strongly in the round table discussion as argued by existing users of experimental methods was the desirability of either designing experiments directly based on a specific ABM structure (rather than trying to use a stripped down – purely behavioural – experiment) or mixing real and simulated participants in richer experimental settings. In line with the enrichment argument put forward by Edmonds, nobody seemed to be using stripped down experiments to specify, calibrate or validate ABM elements piecemeal. In the examples provided by round table participants, experiments corresponding closely to the ABM (and mixing real and simulated participants) seemed particularly valuable in tackling subjects that existing theory had not yet really nailed down or where it was clear that very little of the data needed for a particular ABM was available. But there was no sense that there is a clearly defined set of research designs with associated purposes on which the potential user can draw. (The possible role of experiments in supporting policy was also mentioned but no conclusions were drawn.)

Extracting Rich Data from Experiments

Traditional experiments are time consuming to do, so they are frequently optimised to obtain the maximum power and discrimination between factors of interest. In such situations they will often limit their data collection to what is strictly necessary for testing their hypotheses. Furthermore, it seems to be a hangover from behaviourist psychology that one does not use self-reporting on the grounds that it might be biased or simply involve false reconstruction (rationalisation). From the point of view of building or assessing ABMs this approach involves a wasted opportunity. Due to the flexible nature of ABMs there is a need for as many empirical constraints upon modelling as possible. These constraints can come from theory, evidence or abstract principles (such as simplicity) but should not hinder the design of an ABM but rather act as a check on its outcomes. Game-like situations can provide rich data about what is happening, simultaneously capturing decisions on action, the position and state of players, global game outcomes/scores and what players say to each other (see, for example, Janssen et al. 2010, Lindahl et al. 2021). Often, in social science one might have a survey with one set of participants, interviews with others and longitudinal data from yet others – even if these, in fact, involve the same people, the data will usually not indicate this through consistent IDs. When collecting data from a game (and especially from online games) there is a possibility for collecting linked data with consistent IDs – including interviews – that allows for a whole new level of ABM development and checking.

Standards and Institutional Bootstrapping

This is also a wider problem in newer methods like Agent-Based Modelling. How can we foster agreement about what we are doing (which has to build on clear concepts) and institutionalise those agreements into standards for a field (particularly when there is academic competition and pressure to publish).[v] If certain journals will not publish experiments (or experiments done in certain ways) what can we do about that? JASSS was started because it was so hard to publish ABMs. It has certainly made that easier but is there a cost through less publication in other journals? See, for example, Squazzoni and Casnici (2013). Would it have been better for the rigour and wider acceptance of Agent-Based Modelling if we had met the standards of other fields rather than setting our own? This strategy, harder in the short term, may also have promoted communication and collaboration better in the long term. If reviewing is arbitrary (reviewers do not seem to have a common view of what makes an experiment legitimate) then can that situation be improved (and in particular how do we best go about that with limited resources?) To some extent, normal individualised academic work may achieve progress here (researchers make proposals, dispute and refine them and their resulting quality ensures at least some individualised adoption by other researchers) but there is often an observable gap in performance: Even though most modellers will endorse the value of data for modelling in principle most models are still non-empirical in practice (Angus and Hassani-Mahmooei 2015, Figure 9). The jury is still out on the best way to improve reviewer consistency, use the power of peer review to impose better standards (and thus resolve a collective action problem under academic competition[vi]) and so on but recognising and trying to address these issues is clearly important to the health of experimental methods in Agent-Based Modelling. Since running experiments in association with ABMs is already challenging, adding the problem of arbitrary reviewer standards makes the publication process even harder. This discourages scientists from following this path and therefore retards this kind of research generally. Again, here, useful resources (like the Psychological Science Accelerator, which facilitates greater experimental rigour by various means) were suggested in discussion as raw material for our own improvements to experiments in Agent-Based Modelling.

Another issue with newer methods such as Agent-Based Modelling is the path to legitimation before the wider scientific community. The need to integrate ABMs with experiments does not necessarily imply that the legitimation of the former is achieved by the latter. Experimental economists, for instance, may still argue that (in the investigation of behaviour and its implications for policy issues), experiments and data analysis alone suffice. They may rightly ask: What is the additional usefulness of an ABM? If an ABM always needs to be justified by an experiment and then validated by a statistical model of its output, then the method might not be essential at all. Orthodox economists skip the Agent-Based Modelling part: They build behavioural experiments, gather (rich) data, run econometric models and make predictions, without the need (at least as they see it) to build any computational representation. Of course, the usefulness of models lies in the premise that they may tell us something that experiments alone cannot (see Knudsen et al. 2019). But progress needs to be made in understanding (and perhaps reconciling) these divergent positions. The social simulation community therefore needs to be clearer about exactly what ABMs can contribute beyond the limitations of an experiment, especially when addressing audiences of non-modellers (Ballard et al. 2021). Not only is a model valuable when rigorously validated against data, but also whenever it makes sense of the data in ways that traditional methods cannot.

Where Now?

Researchers usually have more enthusiasm than they have time. In order to make things happen in an academic context it is not enough to have good ideas, people need to sign up and run with them. There are many things that stand a reasonable chance of improving the profile and practice of experiments in Agent-Based Modelling (regular sessions at SSC, systematic reviews, practical guidelines and evaluated case studies, discussion groups, books or journal special issues, training and funding applications that build networks and teams) but to a great extent, what happens will be decided by those who make it happen. The organisers of this round table (Nanda Wijermans and Edmund Chattoe-Brown) are very keen to support and coordinate further activity and this summary of discussions is the first step to promote that. We hope to hear from you.

References

Angus, Simon D. and Hassani-Mahmooei, Behrooz (2015) ‘“Anarchy” Reigns: A Quantitative Analysis of Agent-Based Modelling Publication Practices in JASSS, 2001-2012’, Journal of Artificial Societies and Social Simulation, 18(4), October, article 16, <http://jasss.soc.surrey.ac.uk/18/4/16.html>. doi:10.18564/jasss.2952

Ballard, Timothy, Palada, Hector, Griffin, Mark and Neal, Andrew (2021) ‘An Integrated Approach to Testing Dynamic, Multilevel Theory: Using Computational Models to Connect Theory, Model, and Data’, Organizational Research Methods, 24(2), April, pp. 251-284. doi: 10.1177/1094428119881209

Basole, Rahul C., Bodner, Douglas A. and Rouse, William B. (2013) ‘Healthcare Management Through Organizational Simulation’, Decision Support Systems, 55(2), May, pp. 552-563. doi:10.1016/j.dss.2012.10.012

Boero, Riccardo, Bravo, Giangiacomo, Castellani, Marco and Squazzoni, Flaminio (2010) ‘Why Bother with What Others Tell You? An Experimental Data-Driven Agent-Based Model’, Journal of Artificial Societies and Social Simulation, 13(3), June, article 6, <https://www.jasss.org/13/3/6.html>. doi:10.18564/jasss.1620

Bornstein, Brian H. (1999) ‘The Ecological Validity of Jury Simulations: Is the Jury Still Out?’ Law and Human Behavior, 23(1), February, pp. 75-91. doi:10.1023/A:1022326807441

Burton, Richard M. and Obel, Børge (2018) ‘The Science of Organizational Design: Fit Between Structure and Coordination’, Journal of Organization Design, 7(1), December, article 5. doi:10.1186/s41469-018-0029-2

Derbyshire, James (2020) ‘Answers to Questions on Uncertainty in Geography: Old Lessons and New Scenario Tools’, Environment and Planning A: Economy and Space, 52(4), June, pp. 710-727. doi:10.1177/0308518X19877885

Dinesen, Peter Thisted (2013) ‘Where You Come From or Where You Live? Examining the Cultural and Institutional Explanation of Generalized Trust Using Migration as a Natural Experiment’, European Sociological Review, 29(1), February, pp. 114-128. doi:10.1093/esr/jcr044

Doran, Jim (1998) ‘Simulating Collective Misbelief’, Journal of Artificial Societies and Social Simulation, 1(1), January, article 1, <https://www.jasss.org/1/1/3.html>.

Janssen, Marco A., Holahan, Robert, Lee, Allen and Ostrom, Elinor (2010) ‘Lab Experiments for the Study of Social-Ecological Systems’, Science, 328(5978), 30 April, pp. 613-617. doi:10.1126/science.1183532

Kagel, John H. and Roth, Alvin E. (eds.) (1995) The Handbook of Experimental Economics (Princeton, NJ: Princeton University Press).

Knudsen, Thorbjørn, Levinthal, Daniel A. and Puranam, Phanish (2019) ‘Editorial: A Model is a Model’, Strategy Science, 4(1), March, pp. 1-3. doi:10.1287/stsc.2019.0077

Levine, Gustav and Parkinson, Stanley (1994) Experimental Methods in Psychology (Hillsdale, NJ: Lawrence Erlbaum Associates).

Lindahl, Therese, Janssen, Marco A. and Schill, Caroline (2021) ‘Controlled Behavioural Experiments’, in Biggs, Reinette, de Vos, Alta, Preiser, Rika, Clements, Hayley, Maciejewski, Kristine and Schlüter, Maja (eds.) The Routledge Handbook of Research Methods for Social-Ecological Systems (London: Routledge), pp. 295-306. doi:10.4324/9781003021339-25

Ramanath, Ana Maria and Gilbert, Nigel (2004) ‘The Design of Participatory Agent-Based Social Simulations’, Journal of Artificial Societies and Social Simulation, 7(4), October, article 1, <https://www.jasss.org/7/4/1.html>.

Reypens, Charlotte and Levine, Sheen S. (2018) ‘Behavior in Behavioral Strategy: Capturing, Measuring, Analyzing’, in Behavioral Strategy in Perspective, Advances in Strategic Management Volume 39 (Bingley: Emerald Publishing), pp. 221-246. doi:10.1108/S0742-332220180000039016

Squazzoni, Flaminio and Casnici, Niccolò (2013) ‘Is Social Simulation a Social Science Outstation? A Bibliometric Analysis of the Impact of JASSS’, Journal of Artificial Societies and Social Simulation, 16(1), January, article 10, <http://jasss.soc.surrey.ac.uk/16/1/10.html>. doi:10.18564/jasss.2192

Taillandier, Patrick, Grignard, Arnaud, Marilleau, Nicolas, Philippon, Damien, Huynh, Quang-Nghi, Gaudou, Benoit and Drogoul, Alexis (2019) ‘Participatory Modeling and Simulation with the GAMA Platform’, Journal of Artificial Societies and Social Simulation, 22(2), March, article 3, <https://www.jasss.org/22/2/3.html>. doi:10.18564/jasss.3964

Tykhonov, Dmytro, Jonker, Catholijn, Meijer, Sebastiaan and Verwaart, Tim (2008) ‘Agent-Based Simulation of the Trust and Tracing Game for Supply Chains and Networks’, Journal of Artificial Societies and Social Simulation, 11(3), June, article 1, <https://www.jasss.org/11/3/1.html>.

Vuculescu, Oana (2017) ‘Searching Far Away from the Lamp-Post: An Agent-Based Model’, Strategic Organization, 15(2), May, pp. 242-263. doi:10.1177/1476127016669869

Zelditch, Morris Junior (2007) ‘Laboratory Experiments in Sociology’, in Webster, Murray Junior and Sell, Jane (eds.) Laboratory Experiments in the Social Sciences (New York, NY: Elsevier), pp. 183-197.


Notes

[i] This event was organised (and the resulting article was written) as part of “Towards Realistic Computational Models of Social Influence Dynamics” a project funded through ESRC (ES/S015159/1) by ORA Round 5 and involving Bruce Edmonds (PI) and Edmund Chattoe-Brown (CoI). More about SSC2021 (Social Simulation Conference 2021) can be found at https://ssc2021.uek.krakow.pl

[ii] This issue is actually very challenging for social science more generally. When considering interventions in social systems, knowing and acting might be so deeply intertwined (Derbyshire 2020) that interventions may modify the same behaviours that an experiment is aiming to understand.

[iii] In addition, experiments often require institutional ethics approval (but so do interviews, gaming activities and others sort of empirical research of course), something with which non-empirical Agent-Based Modellers may have little experience.

[iv] Chattoe-Brown had interesting personal experience of this. He took part in a simple team gaming exercise about running a computer firm. The team quickly worked out that the game assumed an infinite return to advertising (so you could have a computer magazine consisting entirely of adverts) independent of the actual quality of the product. They thus simultaneously performed very well in the game from the perspective of an external observer but remained deeply sceptical that this was a good lesson to impart about running an actual firm. But since the coordinators never asked the team members for their subjective view, they may have assumed that the simulation was also a success in its didactic mission.

[v] We should also not assume it is best to set our own standards from scratch. It may be valuable to attempt integration with existing approaches, like qualitative validity (https://conjointly.com/kb/qualitative-validity/) particularly when these are already attempting to be multidisciplinary and/or to bridge the gap between, for example, qualitative and quantitative data.

[vi] Although journals also face such a collective action problem at a different level. If they are too exacting relative to their status and existing practice, researchers will simply publish elsewhere.


Dino Carpentras, Edmund Chattoe-Brown, Bruce Edmonds, Cesar García-Diaz, Christian Kammler, Anna Pagani and Nanda Wijermans (2020) Where Now For Experiments In Agent-Based Modelling? Report of a Round Table as Part of SSC2021. Review of Artificial Societies and Social Simulation, 2nd Novermber 2021. https://rofasss.org/2021/11/02/round-table-ssc2021-experiments/


Does It Take Two (And A Creaky Search Engine) To Make An Outstation? Hunting Highly Cited Opinion Dynamics Articles in the Journal of Artificial Societies and Social Simulation (JASSS)

By Edmund Chattoe-Brown

In an important article, Squazzoni and Casnici (2013) raise the issue of how social simulation (as manifested in the Journal of Artificial Societies and Social Simulation – hereafter JASSS – the journal that has probably published the most of this kind of research for longest) cites and is cited in the wider scientific community. They discuss this in terms of social simulation being a potential “outstation” of social science (but better integrated into physical science and computing). This short note considers the same argument in reverse. As an important site of social simulation research, is it the case that JASSS is effectively representing research done more widely across the sciences?

The method used to investigate this was extremely simple (and could thus easily be extended and replicated). On 28.08.21, using the search term “opinion dynamics” in “all fields”, all sources from Web of Science (www.webofknowledge.com, hereafter WOS) that were flagged as “highly cited” were selected as a sample. For each article (only articles turned out to be highly cited), the title was searched in JASSS and the number of hits recorded. Common sense was applied in this search process to maximise the chances of success. So if a title had two sub clauses, these were searched jointly as quotations (to avoid the “hits” being very sensitive to the reproduction of punctuation linking clauses.) In addition, the title of the journal in which the article appeared was searched to give a wider sense of how well the relevant journal is known is JASSS.

However, now we come to the issue of the creaky search engine (as well as other limitations of quick and dirty searches). Obviously searching for the exact title will not find variants of that title with spelling mistakes or attempts to standardise spelling (i. e. changing behavior to behaviour). Further, it turns out that the Google search engine (which JASSS uses) does not promise the consistency that often seems to be assumed for it (http://jdebp.uk/FGA/google-result-counts-are-a-meaningless-metric.html). For example, when I searched for “SIAM Review” I mostly got 77 hits, rather often 37 hits and very rarely 0 or 1 hits. (PDFs are available for three of these outcomes from the author but the fourth could not be reproduced to be recorded in the time available.) This result occurred when another search took place seconds after the first so it is not, for example, a result of substantive changes to the content of JASSS. To deal with this problem I tried to confirm the presence of a particular article by searching jointly for all its co-authors. Mostly this approach gave a similar result (but where it does not it is noted in the table below). In addition, wherever there were a relatively large number of hits for a specific search, some of these were usually not the ones intended. (For example no hit on the term “global challenges” actually turned out to be for the journal Global Challenges.) In addition, JASSS often gives an oddly inconsistent number of hits for a specific article: It may appear as PDF and HTML as well as in multiple indices or may occur just once. (This discouraged attempts to go from hits to the specific number of unique articles citing these WOS sources. As it turns out, this additional detail would have added little to the headline result.)

The term “opinion dynamics” was chosen somewhat arbitrarily (for reasons connected with other research) and it is not claimed that this term is even close to a definitive way of capturing any models connected with opinion/attitude change. Nonetheless, it is clear that the number of hits and the type of articles reported on WOS (which is curated and quality controlled) are sufficient (and sufficiently relevant) for this to be a serviceable search term to identify a solid field of research in JASSS (and elsewhere). I shall return to this issue.

The results, shown in the table below are striking on several counts. (All these sources are fully cited in the references at the end of this article.) Most noticeably, JASSS is barely citing a significant number of articles that are very widely cited elsewhere. Because these are highly cited in WOS this cannot be because they are too new or too inaccessible. The second point is the huge discrepancy in citation for the one article on the WOS list that appears in JASSS itself (Flache et al. 2017). Thirdly, although some of these articles appear in journals that JASSS otherwise does not cite (like Global Challenges and Dynamic Games and Applications) others appear in journals that are known to JASSS and generally cited (like SIAM Review).

Reference WOS Citations Article Title Hits in JASSS Journal Title Hits in JASSS
Acemoglu and Ozdaglar (2011) 301 0 (1 based on joint authors) 2
Motsch and Tadmor (2014) 214 0 77
Van Der Linden et al. (2017) 191 0 6 (but none for the journal)
Acemoğlu et al. (2013) 186 1 2 (but 1 article)
Proskurnikov et al. (2016) 165 0 9
Dong et al. (2017) 147 0 48 (but rather few for the journal)
Jia et al. (2015) 118 0 77
Dong et al. (2018) 117 0 (1 based on joint authors) 48 (but rather few for the journal)
Flache et al. (2017) 86 58 (17 based on joint authors) N/A
Urena et al. (2019) 72 0 6
Bu et al. (2020) 56 0 5
Zhang et al. (2020) 55 0 33 (but only some of these are for the journal)
Xiong et al. (2020) 28 0 1
Carrillo et al. (2020) 13 0 0

One possible interpretation of this result is simply that none of the most highly cited articles in WOS featuring the term “opinion dynamics” happen to be more than incidentally relevant to the scientific interests of JASSS. On consideration, however, this seems a rather improbable coincidence. Firstly, these articles were chosen exactly because they are highly cited so we would have to explain how they could be perceived as so useful generally but specifically not in JASSS. Secondly, the same term (“opinion dynamics”) consistently generates 254 hits in JASSS, suggesting that the problem isn’t a lack of overlap in terminology or research interests.

This situation, however, creates a problem for more conclusive explanation. The state of affairs here is not that these articles are being cited and then rejected on scientific grounds given the interests of JASSS (thus providing arguments I could examine). It is that they are barely being cited at all. Unfortunately, it is almost impossible to establish why something is not happening. Perhaps JASSS authors are not aware of these articles to begin with. Perhaps they are aware but do not see the wider scientific value of critiquing them or attempting to engage with their irrelevance in print.

But, given that the problem is non citation, my concern can be made more persuasive (perhaps as persuasive as it can be given problems of convincingly explaining an absence) by investigating the articles themselves. (My thanks are due to Bruce Edmonds for encouraging me to strengthen the argument in this way.) There are definitely some recurring patterns in this sample. Firstly, a significant proportion of the articles are highly mathematical and, therefore (as Agent-Based Modelling often criticises) rely on extreme simplifying assumptions and toy examples. Even here, however, it is not self-evident that such articles should not be cited in JASSS merely because they are mathematical. JASSS has itself published relatively mathematical articles and, if an article contains a mathematical model that could be “agentised” (thus relaxing its extreme assumptions) which is no less empirical than similar models in JASSS (or has particularly interesting behaviours) then it is hard to see why this should not be discussed by at least a few JASSS authors. A clear example of this is provided by Acemoğlu et al. (2013) which argues that existing opinion dynamics models fail to produce the ongoing fluctuations of opinion observed in real data (see, for example, Figures 1-3 in Chattoe-Brown 2014 which also raises concerns about the face validity of popular social simulations of opinion dynamics). In fact, the assumptions of this model could easily be questioned (and real data involves turning points and not just fluctuations) but the point is that JASSS articles are not citing it and rejecting it based on argument but simply not citing it. A model capable of generating ongoing opinion fluctuations (however imperfect) is simply too important to the current state of opinion dynamics research in social simulation not to be considered at all. Another (though less conclusive) example is Motsch and Tadmor (2014) which presents a model suggesting (counter intuitively) that interaction based on heterophily can better achieve consensus than interaction based on homophily. Of course one can reject such an assumption on empirical grounds but JASSS is not currently doing that (and in fact the term heterophily is unknown in the journal except for the title of a cited article.)

Secondly, there are also a number of articles which, while not providing important results seem no less plausible or novel than typical OD articles that are published in JASSS. For example, Jia et al. (2015) add self-appraisal and social power to a standard OD model. Between debates, agents amend the efficacy they believe that they and others have in terms of swaying the outcome and take that into account going forward. Proskurnikov et al. (2016) present the results of a model in which agents can have negative ties with each other (as well as the more usual positive ones) and thus consider the coevolution of positive/negative sentiments and influence (describing what they call hostile camps i. e. groups with positive ties to each other and negative ties to other groups). This is distinct from the common repulsive effect in OD models where agents do not like the opinions of others (rather than disliking the others themselves.)

Finally, both Dong et al. (2017) and Zhang et al. (2020) reach for the idea (through modelling) that experts and leaders in OD models may not just be randomly scattered through the population as types but may exist because of formal organisations or accidents of social structure: This particular agent is either deliberately appointed to have more influence or happens to have it because of their network position.

On a completely different tack, two articles (Dong et al. 2018 and Acemoglu and Ozdaglar 2011) are literature reviews or syntheses on relevant topics and it is hard to see how such broad ranging articles could have so little value to OD research in JASSS.

It will be admitted that some of the articles in the sample are hard to evaluate with certainty. Mathematical approaches often seem to be more interested in generating mathematics than in justifying its likely value. This is particularly problematic when combined with a suggestion that the product of the research may be instrumental algorithms (designed to get things done) rather than descriptive ones (designed to understand social behaviour). An example of this is several articles which talk about achieving consensus without really explaining whether this is a technical goal (for example in a neural network) or a social phenomenon and, if the latter, whether this places constraints on what it legitimate: You can reach consensus by debate but not by shooting dissenters!

But as well as specific ideas in specific models, this sample of articles also suggest a different emphasis from those currently found within JASSS OD research. For example, there is much more interest in deliberately achieving consensus (and the corresponding hazards of manipulation or misinformation impeding that.) Reading these articles collectively gives a sense that JASSS OD models are very much liberal democratic: Agents honestly express their views (or at most are somewhat reticent to protect themselves.) They decently expect the will of the people to prevail. They do not lie strategically to sway the influential, spread rumours to discredit the opinions of opponents or flood the debate with bots. Again, this darker vision is no more right a priori than the liberal democratic one but JASSS should at least be engaging with articles modelling (or providing data on – see Van Der Linden et al. 2017) such phenomena in an OD context. (Although misinformation is mentioned in some OD articles in JASSS it does not seem to be modelled. There also seems to be another surprising glitch in the search engine which considers the term “fake news” to be a hit for misinformation!) This also puts a new slant on an ongoing challenge in OD research, identifying a plausible relationship between fact and opinion. Is misinformation a different field of research (on the grounds that opinions can never be factually wrong) or is it possible for the misinformed to develop mis-opinions? (Those that they would change if what they knew changed.) Is it really the case that Brexiteers, for example, are completely indifferent to the economic consequences which will reveal themselves or did they simply have mistaken beliefs about how high those costs might turn out to be which will cause them to regret their decision at some later stage?

Thus to sum up, while some of the articles in the sample can be dismissed as either irrelevant to JASSS or having a potential relevance that is hard to establish, the majority cannot reasonably be regarded in this way (and a few are clearly important to the existing state of OD research.) While we cannot explain why these articles are not in fact cited, we can thus call into question one possible (Panglossian) explanation for the observed pattern (that they are not cited because they have nothing to contribute).

Apart from the striking nature of the result and its obvious implication (if social simulators want to be cited more widely they need to make sure they are also citing the work of others appropriately) this study has two wider (related) implications for practice.

Firstly, systematic literature reviewing (see, for example, Hansen et al. 2019 – not published in JASSS) needs to be better enforced in social simulation: “Systematic literature review” gets just 7 hits in JASSS. It is not enough to cite just what you happen to have read or models that resemble your own, you need to be citing what the community might otherwise not be aware of or what challenges your own model assumptions. (Although, in my judgement, key assumptions of Acemoğlu et al. 2013 are implausible I don’t think that I could justify non subjectively that they are any more implausible than those of those of the Zaller-Deffuant model – Malarz et al. 2011 – given the huge awareness discrepancy which the two models manifest in social simulation.)

Secondly, we need to rethink the nature of literature reviewing as part of progressive research. I have used “opinion dynamics” here not because it is the perfect term to identify all models of opinion and attitude change but because it throws up enough hits to show that this term is widely used in social simulation. Because I have clearly stated my search term, others can critique it and extend my analysis using other relevant terms like “opinion change” or “consensus formation”. A literature review that is just a bunch of arbitrary stuff cannot be critiqued or improved systematically (rather than nit-picked for specific omissions – as reviewers often do – and even then the critique can’t tell what should have been included if there are no clearly stated search criteria.) It should not be possible for JASSS (and the social simulation community it represents) simply to disregard articles as potentially important in their implications for OD as Acemoğlu et al. (2013). Even if this article turned out to be completely wrong-headed, we need to have enough awareness of it to be able to say why before setting it aside. (Interestingly, the one citation it does receive in JASSS can be summarised as “there are some other model broadly like this” with no detailed discussion at all – and thus no clear statement of how the model presented in the citing article adds to previous models – but uninformative citation is a separate problem.)

Acknowledgements

This article as part of “Towards Realistic Computational Models of Social Influence Dynamics” a project funded through ESRC (ES/S015159/1) by ORA Round 5.

References

Acemoğlu, Daron and Ozdaglar, Asuman (2011) ‘Opinion Dynamics and Learning in Social Networks’, Dynamic Games and Applications, 1(1), March, pp. 3-49. doi:10.1007/s13235-010-0004-1

Acemoğlu, Daron, Como, Giacomo, Fagnani, Fabio and Ozdaglar, Asuman (2013) ‘Opinion Fluctuations and Disagreement in Social Networks’, Mathematics of Operations Research, 38(1), February, pp. 1-27. doi:10.1287/moor.1120.0570

Bu, Zhan, Li, Hui-Jia, Zhang, Chengcui, Cao, Jie, Li, Aihua and Shi, Yong (2020) ‘Graph K-Means Based on Leader Identification, Dynamic Game, and Opinion Dynamics’, IEEE Transactions on Knowledge and Data Engineering, 32(7), July, pp. 1348-1361. doi:10.1109/TKDE.2019.2903712

Carrillo, J. A., Gvalani, R. S., Pavliotis, G. A. and Schlichting, A. (2020) ‘Long-Time Behaviour and Phase Transitions for the Mckean–Vlasov Equation on the Torus’, Archive for Rational Mechanics and Analysis, 235(1), January, pp. 635-690. doi:10.1007/s00205-019-01430-4

Chattoe-Brown, Edmund (2014) ‘Using Agent Based Modelling to Integrate Data on Attitude Change’, Sociological Research Online, 19(1), February, article 16, <http://www.socresonline.org.uk/19/1/16.html&gt;. doi:10.5153/sro.3315

Dong, Yucheng, Ding, Zhaogang, Martínez, Luis and Herrera, Francisco (2017) ‘Managing Consensus Based on Leadership in Opinion Dynamics’, Information Sciences, 397-398, August, pp. 187-205. doi:10.1016/j.ins.2017.02.052

Dong, Yucheng, Zhan, Min, Kou, Gang, Ding, Zhaogang and Liang, Haiming (2018) ‘A Survey on the Fusion Process in Opinion Dynamics’, Information Fusion, 43, September, pp. 57-65. doi:10.1016/j.inffus.2017.11.009

Flache, Andreas, Mäs, Michael, Feliciani, Thomas, Chattoe-Brown, Edmund, Deffuant, Guillaume, Huet, Sylvie and Lorenz, Jan (2017) ‘Models of Social Influence: Towards the Next Frontiers’, Journal of Artificial Societies and Social Simulation, 20(4), October, article 2, <http://jasss.soc.surrey.ac.uk/20/4/2.html&gt;. doi:10.18564/jasss.3521

Hansen, Paula, Liu, Xin and Morrison, Gregory M. (2019) ‘Agent-Based Modelling and Socio-Technical Energy Transitions: A Systematic Literature Review’, Energy Research and Social Science, 49, March, pp. 41-52. doi:10.1016/j.erss.2018.10.021

Jia, Peng, MirTabatabaei, Anahita, Friedkin, Noah E. and Bullo, Francesco (2015) ‘Opinion Dynamics and the Evolution of Social Power in Influence Networks’, SIAM Review, 57(3), pp. 367-397. doi:10.1137/130913250

Malarz, Krzysztof, Gronek, Piotr and Kulakowski, Krzysztof (2011) ‘Zaller-Deffuant Model of Mass Opinion’, Journal of Artificial Societies and Social Simulation, 14(1), 2, <https://www.jasss.org/14/1/2.html&gt;. doi:10.18564/jasss.1719

Motsch, Sebastien and Tadmor, Eitan (2014) ‘Heterophilious Dynamics Enhances Consensus’, SIAM Review, 56(4), pp. 577-621. doi:10.1137/120901866

Proskurnikov, Anton V., Matveev, Alexey S. and Cao, Ming (2016) ‘Opinion Dynamics in Social Networks With Hostile Camps: Consensus vs. Polarization’, IEEE Transactions on Automatic Control, 61(6), June, pp. 1524-1536. doi:10.1109/TAC.2015.2471655

Squazzoni, Flaminio and Casnici, Niccolò (2013) ‘Is Social Simulation a Social Science Outstation? A Bibliometric Analysis of the Impact of JASSS’, Journal of Artificial Societies and Social Simulation, 16(1), 10, <http://jasss.soc.surrey.ac.uk/16/1/10.html&gt;. doi:10.18564/jasss.2192

Ureña, Raquel, Chiclana, Francisco, Melançon, Guy and Herrera-Viedma, Enrique (2019) ‘A Social Network Based Approach for Consensus Achievement in Multiperson Decision Making’, Information Fusion, 47, May, pp. 72-87. doi:10.1016/j.inffus.2018.07.006

Van Der Linden, Sander, Leiserowitz, Anthony, Rosenthal, Seth and Maibach, Edward (2017) ‘Inoculating the Public against Misinformation about Climate Change’, Global Challenges, 1(2), 27 February, article 1600008. doi:10.1002/gch2.201600008

Xiong, Fei, Wang, Ximeng, Pan, Shirui, Yang, Hong, Wang, Haishuai and Zhang, Chengqi (2020) ‘Social Recommendation With Evolutionary Opinion Dynamics’, IEEE Transactions on Systems, Man, and Cybernetics: Systems, 50(10), October, pp. 3804-3816. doi:10.1109/TSMC.2018.2854000

Zhang, Zhen, Gao, Yuan and Li, Zhuolin (2020) ‘Consensus Reaching for Social Network Group Decision Making by Considering Leadership and Bounded Confidence’, Knowledge-Based Systems, 204, 27 September, article 106240. doi:10.1016/j.knosys.2020.106240


Chattoe-Brown, E. (2021) Does It Take Two (And A Creaky Search Engine) To Make An Outstation? Hunting Highly Cited Opinion Dynamics Articles in the Journal of Artificial Societies and Social Simulation (JASSS). Review of Artificial Societies and Social Simulation, 19th August 2021. https://rofasss.org/2021/08/19/outstation/


 

The role of population scale in compartmental models of COVID-19 transmission

By Christopher J. Watts1,*, Nigel Gilbert2, Duncan Robertson3, 4, Laurence T. Droy5, Daniel Ladley6and Edmund Chattoe-Brown5

*Corresponding author, 12 Manor Farm Cottages, Waresley, Sandy, SG19 3BZ, UK, 2Centre for Research in Social Simulation (CRESS), University of Surrey, Guildford GU2 7XH, UK, 3School of Business and Economics, Loughborough University, Loughborough, UK, 4St Catherine’s College, University of Oxford, Oxford, UK, 5School of Media, Communication and Sociology, University of Leicester, UK, 6University of Leicester School of Business, University of Leicester, Leicester, LE17RH, UK

(A contribution to the: JASSS-Covid19-Thread)

Compartmental models of COVID-19 transmission have been used to inform policy, including the decision to temporarily reduce social contacts among the general population (“lockdown”). One such model is a Susceptible-Exposed-Infectious-Removed (SEIR) model developed by a team at the London School of Hygiene and Tropical Medicine (hereafter, “the LSHTM model”, Davies et al., 2020a). This was used to evaluate the impact of several proposed interventions on the numbers of cases, deaths, and intensive care unit (ICU) hospital beds required in the UK. We wish here to draw attention to behaviour common to this and other compartmental models of diffusion, namely their sensitivity to the size of the population simulated and the number of seed infections within that population. This sensitivity may compromise any policy advice given.

We therefore describe below the essential details of the LSHTM model, our experiments on its sensitivity, and why they matter to its use in policy making.

The LSHTM model

Compartmental models of disease transmission divide members of a population according to their disease states, including at a minimum people who are “susceptible” to a disease, and those who are “infectious”. Susceptible individuals make social contact with others within the same population at given rates, with no preference for the other’s disease state, spatial location, or social networks (the “universal mixing” assumption). Social contacts result in infections with a chance proportional to the fraction of the population who are currently infectious. Perhaps to reduce the implausibility of the universal mixing assumption, the LSHTM model is run for each of 186 county-level administrative units (“counties”, having an average size of 357,000 people), instead of a single run covering the whole UK population (66.4 million). Each county receives the same seed infection schedule: two new infections per day for 28 days. The 186 county time series are then summed to form a time series for the UK. There are no social contacts between counties, and the 186 county-level runs are independent of each other. Outputs from the model include total and peak cases and deaths, ICU and non-ICU hospital bed occupancy, and the time to peak cases, all reported for the UK as a whole.

Interventions are modelled as 12-week reductions in contact rates, and, in the first experiment, scheduled to commence 6 weeks prior to the peak in UK cases with no intervention. Further experiments shift the start of the intervention, and trigger the intervention upon reaching a given number of ICU beds, rather than a specific time.

Studying sensitivity to population size

The 186 counties vary in their population sizes, from Isles of Scilly (2,242 people) to West Midlands (2.9 million). We investigated whether the variation in population size led to differences in model behaviour. The LSHTM model files were cloned from https://github.com/cmmid/covid-UK , while the data analysis was performed using our own scripts posted at https://github.com/innovative-simulator/PopScaleCompartmentModels .

A graph showing Peak week infections against population size (on a log scale). The peak week looks increasing linear (with the log population scale), but there is a uniform increase in peak week with more seed infections.The figure above shows the results of running the LSHTM model with populations of various sizes, each point being an average of 10 repetitions. The time, in weeks, to the peak in cases forms a linear trend with the base-10 logarithm of population. A linear regression line fitted to these points gives Peak Week = 2.70 log10(Population) – 2.80, with R2 = 0.999.

To help understand this relationship, we then compared the seeding used by the LSHTM team, i.e. 2 infectious persons per day for 28 days, to two forms of reduced seeding, 1 per day for 28 days, and 2 per day for 14 days. Halving the seeding is similar in effect, but not identical to, doubling the population size.

Deterministic versions of other compartmental models of transmission (SIR, SEIR, SI) confirmed the relation between population size and time of occurrence to be a common feature of such models. See the R and Excel files at: https://github.com/innovative-simulator/PopScaleCompartmentModels .

For the simplest, the SI model, the stock of infectious people is described by the logistic function.I(t)=N/(1+exp(-u*C*(t-t*)))Here N is the population size, u susceptibility, and C the contact rate. If I(0)=s, the number of seed infections, then it can be shown that the peak in new infections, I(t*), occurs at timet*=ln(N/s-1)/(u*C)

Hence, for N/s >> 1, the time to peak cases, t*, correlates well with log10N/s.

As well as peak cases, analogous sensitivity was found for the timing of peaks in infections and hospital admissions, and for reaching critical levels, such as the hospital bed capacity as a proportion of the population. In contrast, the heights of peaks, and totals of cases, deaths and beds were constant percentages of population when population size was varied.

Why the unit of population matters

Davies et al. (2020a) make forecasts of both the level of peak cases and the timing of their occurrence. Despite showing that two counties can vary in their results (Davies et al., 2020a, p. 6), and mentioning in the supplementary material some effects of changing the seeding schedule (Davies et al., 2020b, p. 5), they do not mention any sensitivity to population size. But, as we have shown here, given the same number and timing of seed infections, the county with the smallest population will peak in cases earlier than the one with the largest. This sensitivity to population size affects the arguments of Davies et al. in several ways.

Firstly, Davies et al. produce their forecasts for the UK by summing county-level time series. But counties with out-of-sync peaks will sum to produce a shorter, flatter peak for the UK, than would have been achieved by synchronous county peaks. Thus the forecasts of peak cases for the UK are being systematically biased down.

Secondly, timing is important for the effectiveness of the interventions. As Davies et al. note in relation to their experiment on shifting the start time of the intervention, an intervention can be too early or too late. It is too early if, when it ends after 12 weeks, the majority of the population is still susceptible to any remaining infectious cases, and a serious epidemic can still occur. At the other extreme, an intervention can be too late if it starts when most of the epidemic has already occurred.

A timing problem also threatens if the intervention is triggered by the occupancy of ICU beds reaching some critical level. This level will be reached for the UK or average county later than for a small county. Thus the problem extends beyond the timing of peaks to affect other aspects of a policy supported by the model.

Our results imply that an intervention timed optimally for a UK-level, or average county-level, cases peak, as well as an intervention triggered by a UK-level beds occupancy threshold, may be less effective for counties with far-from-average sizes.

There are multiple ways of resolving these issues, including re-scaling seed infections in line with size of population unit, simulating the UK directly rather than as a sum of counties, and rejecting compartmental models in favour of network- or agent-based models. A discussion of the respective pros and cons of these alternatives requires a longer paper. For now, we note that compartmental models remain quick and cheap to design, fit, and study. The issues with Davies et al. (2020a) we have drawn attention to here highlight (1) the importance of adequate sensitivity testing, (2) the need for care when choosing at which scale to model and how to seed an infection, and (3) the problems that can stem from uniform national policy interventions, rather than ones targeted at a more local level.

References

Davies, N. G., Kucharski, A. J., Eggo, R. M., Gimma, A., Edmunds, W. J., Jombart, T., . . . Liu, Y. (2020a). Effects of non-pharmaceutical interventions on COVID-19 cases, deaths, and demand for hospital services in the UK: a modelling study. The Lancet Public Health, 5(7), e375-e385. doi:10.1016/S2468-2667(20)30133-X

Davies, N. G., Kucharski, A. J., Eggo, R. M., Gimma, A., Edmunds, W. J., Jombart, T., . . . Liu, Y. (2020b). Supplement to Davies et al. (2020b). https://www.thelancet.com/cms/10.1016/S2468-2667(20)30133-X/attachment/cee85e76-cffb-42e5-97b6-06a7e1e2379a/mmc1.pdf


Watts, C.J., Gilbert, N., Robertson, D., Droy, L.T., Ladley, D and Chattoe-Brown, E. (2020) The role of population scale in compartmental models of COVID-19 transmission. Review of Artificial Societies and Social Simulation, 14th August 2020. https://rofasss.org/2020/08/14/role-population-scale/


 

A Bibliography of ABM Research Explicitly Comparing Real and Simulated Data for Validation

By Edmund Chattoe-Brown

The Motivation

Research that confronts models with data is still sufficiently rare that it is hard to get a representative sense of how it is done and how convincing the results are simply by “background reading”. One way to advance good quality empirical modelling is therefore simply to make it more visible in quantity. With this in mind I have constructed (building on the work of Angus and Hassani-Mahmooei 2015) the first version of a bibliography listing all ABM attempting empirical validation in JASSS between 1998 and 2019 (along with a few other example) – which generates 68 items in all. Each entry gives a full reference and also describes what comparisons are made and where in the article they occur. In addition the document contains a provisional bibliography of articles giving advice or technical support to validation and lists three survey articles that categorise large samples of simulations by their relationships to data (which served as actual or potential sources for the bibliography).

With thanks to Bruce Edmonds, this first version of the bibliography has been made available as a Centre for Policy Modelling Discussion Paper CPM-20-216, which can be downloaded http://cfpm.org/discussionpapers/256.

The Argument

It may seem quite surprising to focus only on validation initially but there is an argument (Chattoe-Brown 2019) which says that this is a more fundamental challenge to the quality of a model than calibration. A model that cannot track real data well, even when its parameters are tuned to do so is clearly a fundamentally inadequate model. Only once some measure of validation has been achieved can we decide how “convincing” it is (comparing independent empirical calibration with parameter tuning for example). Arguably, without validation, we cannot really be sure whether a model tells us anything about the real world at all (no matter how plausible any narrative about its assumptions may appear). This can be seen as a consequence of the arguments about complexity routinely made by ABM practitioners as the plausibility of the assumptions does not map intuitively onto the plausibility of the outputs.

The Uses

Although these are covered in the preface to the bibliography in greater detail, such a sample has a number of scientific uses which I hope will form the basis for further research.

  • To identify (and justify) good and bad practice, thus promoting good practice.
  • To identify (and then perhaps fill) gaps in the set of technical tools needed to support validation (for example involving particular sorts of data).
  • To test the feasibility and value of general advice offered on validation to date and refine it in the face of practical challenges faced by analysis of real cases.
  • To allow new models to demonstrably outperform the levels of validation achieved by existing models (thus creating the possibility for progressive empirical research in ABM).
  • To support agreement about the effective use of the term validation and to distinguish it from related concepts (like verification) and potentially unhelpful (for example ambiguous or rhetorically loaded) uses

The Plan

Because of the labour involved and the diversity of fields in which ABM have now been used over several decades, an effective bibliography on this kind cannot be the work of a single author (or even a team of authors). My plan is thus to solicit (fully credited) contributions and regularly release new versions of the bibliography – with new co-authors as appropriate. (This publishing model is intended to maintain the quality and suitability for citation of the resulting document relative to the anarchy that sometimes arises in genuine communal authorship!) All of the following contributions will be gratefully accepted for the next revision (on which I am already working myself in any event)

  • References to new surveys or literature reviews that categorise significant samples of ABM research by their relationship to data.
  • References for proposed new entries to the bibliography in as much detail as possible.
  • Proposals to delete incorrectly categorised entries. (There are a small number of cases where I have found it very difficult to establish exactly what the authors did in the name of validation, partly as a result of confusing or ambiguous terminology.)
  • Proposed revisions to incorrect or “unfair” descriptions of existing entries (ideally by the authors of those pieces).
  • Offers of collaboration for a proposed companion bibliography on calibration. Ultimately this will lead to a (likely very small) sample of calibrated and validated ABM (which are often surprisingly little cited given their importance to the credibility of the ABM “project” – see, for example, Chattoe-Brown (2018a, 2018b).

Acknowledgements

This article as part of “Towards Realistic Computational Models of Social Influence Dynamics” a project funded through ESRC (ES/S015159/1) by ORA Round 5.

References

Angus, Simon D. and Hassani-Mahmooei, Behrooz (2015) ‘“Anarchy” Reigns: A Quantitative Analysis of Agent-Based Modelling Publication Practices in JASSS, 2001-2012’, Journal of Artificial Societies and Social Simulation, 18(4), October, article 16. <http://jasss.soc.surrey.ac.uk/18/4/16.html> doi:10.18564/jasss.2952

Chattoe-Brown, Edmund (2018a) ‘Query: What is the Earliest Example of a Social Science Simulation (that is Nonetheless Arguably an ABM) and Shows Real and Simulated Data in the Same Figure or Table?’ Review of Artificial Societies and Social Simulation, 11 June. https://rofasss.org/2018/06/11/ecb/

Chattoe-Brown, Edmund (2018b) ‘A Forgotten Contribution: Jean-Paul Grémy’s Empirically Informed Simulation of Emerging Attitude/Career Choice Congruence (1974)’, Review of Artificial Societies and Social Simulation, 1 June. https://rofasss.org/2018/06/01/ecb/

Chattoe-Brown, Edmund (2019) ‘Agent Based Models’, in Atkinson, Paul, Delamont, Sara, Cernat, Alexandru, Sakshaug, Joseph W. and Williams, Richard A. (eds.) SAGE Research Methods Foundations. doi:10.4135/9781526421036836969


Chattoe-Brown, E. (2020) A Bibliography of ABM Research Explicitly Comparing Real and Simulated Data for Validation. Review of Artificial Societies and Social Simulation, 12th June 2020. https://rofasss.org/2020/06/12/abm-validation-bib/


 

The Policy Context of Covid19 Agent-Based Modelling

By Edmund Chattoe-Brown

(A contribution to the: JASSS-Covid19-Thread)

In the recent discussions about the role of ABM and COVID, there seems to be an emphasis on the purely technical dimensions of modelling. This obviously involves us “playing to our strengths” but unfortunately it may reduce the effectiveness that our potential policy contributions can make. Here are three contextual aspects of policy for consideration to provide a contrast/corrective.

What is “Good” Policy?

Obviously from a modelling perspective good policy involves achieving stated goals. So a model that suggests a lower death rate (or less taxing of critical care facilities) under one intervention rather than another is a potential argument for that intervention. (Though of course how forceful the argument is depends on the quality of the model.) But the problem is that policy is predominantly a political and not a technical process (related arguments are made by Edmonds 2020). The actual goals by which a policy is evaluated may not be limited to the obvious technical ones (even if that is what we hear most about in the public sphere) and, most problematically, there may be goals which policy makers are unwilling to disclose. Since we do not know what these goals are, we cannot tell whether their ends are legitimate (having to negotiate privately with the powerful to achieve anything) or less so (getting re-elected as an end in itself).

Of course, by its nature (being based on both power and secrecy), this problem may be unfixable but even awareness of it may change our modelling perspective in useful ways. Firstly, when academic advice is accused of irrelevance, the academics can only ever be partly to blame. You can only design good policy to the extent that the policy maker is willing to tell you the full evaluation function (to the extent that they know it of course). Obviously, if policy is being measured by things you can’t know about, your advice is at risk of being of limited value. Secondly, with this is mind, we may be able to gain some insight into the hidden agenda of policy by looking at what kind of suggestions tend to be accepted and rejected. Thirdly, once we recognise that there may be “unknown unknowns” we can start to conjecture intelligently about what these could be and take some account of them in our modelling strategies. For example, how many epidemic models consider the financial costs of interventions even approximately? Is the idea that we can and will afford whatever it takes to reduce deaths a blind spot of the “medical model?”

When and How to Intervene

There used to be an (actually rather odd) saying: “You can’t get a baby in a month by making nine women pregnant”. There has been a huge upsurge in interest regarding modelling and its relationship to policy since start of the COVID crisis (of which this theme is just one example) but realising the value of this interest currently faces significant practical problems. Data collection is even harder than usual (as is scholarship in general), there is a limit to how fast good research can ever be done, peer review takes time and so on. The question here is whether any amount of rushing around at the present moment will compensate for neglected activities when scholarship was easier and had more time (an argument also supported by Bithell 2018). The classic example is the muttering in the ABM community about the Ferguson model being many thousands of lines of undocumented C code. Now we are in a crisis, even making the model available was a big ask, let alone making it easier to read so that people might “heckle” it. But what stopped it being available, documented, externally validated and so on before COVID? What do we need to do so that next time there is a pandemic crisis, which there surely will be, “we” (the modelling community very broadly defined) are able to offer the government a “ready” model that has the best features of various modelling techniques, evidence of unfudgeable quality against data, relevant policy scenarios and so on? (Specifically, how will ABM make sure it deserves to play a fit part in this effort?) Apart from the models themselves, what infrastructures, modelling practices, publishing requirements and so on do we need to set up and get working well while we have the time? In practice, given the challenges of making effective contributions right now (and the proliferation of research that has been made available without time for peer review may be actively harmful), this perspective may be the most important thing we can realistically carry into the “post lockdown” world.

What Happens Afterwards?

ABM has taken such a long time to “get to” policy based on data that looking further than the giving of such advice simply seems to have been beyond us. But since policy is what actually happens, we have a serious problem with counterfactuals. If the government decides to “flatten the curve” rather than seek “herd immunity” then we know how the policy implemented relates to the model “findings” (for good or ill) but not how the policy that was not implemented does. Perhaps the outturn of the policy that looked worse in the model would actually have been better had it been implemented?

Unfortunately (this is not a typo), we are about to have an unprecedently large social data set of comparative experiments in the nature and timing of epidemiological interventions, but ABM needs to be ready and willing to engage with this data. I think that ABM probably has a unique contribution to make in “endogenising” the effects of policy implementation and compliance (rather than seeing these, from a “model fitting” perspective, as structural changes to parameter values) but to make this work, we need to show much more interest in data than we have to date.

In 1971, Dutton and Starbuck, in a worryingly neglected article (cited only once in JASSS since 1998 and even then not in respect of model empirics) reported that 81% of the models they surveyed up to 1969 could not achieve even qualitative measurement in both calibration and validation (with only 4% achieving quantitative measurement in both). As a very rough comparison (but still the best available), Angus and Hassani-Mahmooei (2015) showed that just 13% of articles in JASSS published between 2010 and 2012 displayed “results elements” both from the simulation and using empirical material (but the reader cannot tell whether these are qualitative or quantitative elements or whether their joint presence involves comparison as ABM methodology would indicate). It would be hard to make the case that the situation in respect to ABM and data has therefore improved significantly in 4 decades and it is at least possible that it has got worse!

For the purposes of policy making (in the light of the comments above), what matters of course is not whether the ABM community believes that models without data continue to make a useful contribution but whether policy makers do.

References

Angus, S. D. and Hassani-Mahmooei, B. (2015) “Anarchy” Reigns: A Quantitative Analysis of Agent-Based Modelling Publication Practices in JASSS, 2001-2012, Journal of Artificial Societies and Social Simulation, 18(4), 16. doi:10.18564/jasss.2952

Bithell, M. (2018) Continuous model development: a plea for persistent virtual worlds, Review of Artificial Societies and Social Simulation, 22nd August 2018. https://rofasss.org/2018/08/22/mb

Dutton, John M. and Starbuck, William H. (1971) Computer Simulation Models of Human Behavior: A History of an Intellectual Technology. IEEE Transactions on Systems, Man, and Cybernetics, SMC-1(2), 128–171. doi:10.1109/tsmc.1971.4308269

Edmonds, B. (2020) What more is needed for truly democratically accountable modelling? Review of Artificial Societies and Social Simulation, 2nd May 2020. https://rofasss.org/2020/05/02/democratically-accountable-modelling/


Chattoe-Brown, E. (2020) The Policy Context of Covid19 Agent-Based Modelling. Review of Artificial Societies and Social Simulation, 4th May 2020. https://rofasss.org/2020/05/04/policy-context/


 

Cherchez Le RAT: A Proposed Plan for Augmenting Rigour and Transparency of Data Use in ABM

By Sebastian Achter, Melania Borit, Edmund Chattoe-Brown, Christiane Palaretti and Peer-Olaf Siebers

The initiative presented below arose from a Lorentz Center workshop on Integrating Qualitative and Quantitative Evidence using Social Simulation (8-12 April 2019, Leiden, the Netherlands). At the beginning of this workshop, the attenders divided themselves into teams aiming to work on specific challenges within the broad domain of the workshop topic. Our team took up the challenge of looking at “Rigour, Transparency, and Reuse”. The aim that emerged from our initial discussions was to create a framework for augmenting rigour and transparency (RAT) of data use in ABM when both designing, analysing and publishing such models.

One element of the framework that the group worked on was a roadmap of the modelling process in ABM, with particular reference to the use of different kinds of data. This roadmap was used to generate the second element of the framework: A protocol consisting of a set of questions, which, if answered by the modeller, would ensure that the published model was as rigorous and transparent in terms of data use, as it needs to be in order for the reader to understand and reproduce it.

The group (which had diverse modelling approaches and spanned a number of disciplines) recognised the challenges of this approach and much of the week was spent examining cases and defining terms so that the approach did not assume one particular kind of theory, one particular aim of modelling, and so on. To this end, we intend that the framework should be thoroughly tested against real research to ensure its general applicability and ease of use.

The team was also very keen not to “reinvent the wheel”, but to try develop the RAT approach (in connection with data use) to augment and “join up” existing protocols or documentation standards for specific parts of the modelling process. For example, the ODD protocol (Grimm et al. 2010) and its variants are generally accepted as the established way of documenting ABM but do not request rigorous documentation/justification of the data used for the modelling process.

The plan to move forward with the development of the framework is organised around three journal articles and associated dissemination activities:

  • A literature review of best (data use) documentation and practice in other disciplines and research methods (e.g. PRISMA – Preferred Reporting Items for Systematic Reviews and Meta-Analyses)
  • A literature review of available documentation tools in ABM (e.g. ODD and its variants, DOE, the “Info” pane of NetLogo, EABSS)
  • An initial statement of the goals of RAT, the roadmap, the protocol and the process of testing these resources for usability and effectiveness
  • A presentation, poster, and round table at SSC 2019 (Mainz)

We would appreciate suggestions for items that should be included in the literature reviews, “beta testers” and critical readers for the roadmap and protocol (from as many disciplines and modelling approaches as possible), reactions (whether positive or negative) to the initiative itself (including joining it!) and participation in the various activities we plan at Mainz. If you are interested in any of these roles, please email Melania Borit (melania.borit@uit.no).

References

Grimm, V., Berger, U., DeAngelis, D. L., Polhill, J. G., Giske, J. and Railsback, S. F. (2010) ‘The ODD Protocol: A Review and First Update’, Ecological Modelling, 221(23):2760–2768. doi:10.1016/j.ecolmodel.2010.08.019


Achter, S., Borit, M., Chattoe-Brown, E., Palaretti, C. and Siebers, P.-O.(2019) Cherchez Le RAT: A Proposed Plan for Augmenting Rigour and Transparency of Data Use in ABM. Review of Artificial Societies and Social Simulation, 4th June 2019. https://rofasss.org/2019/06/04/rat/


 

Query: What is the earliest example of a social science simulation (that is nonetheless arguably an ABM) and shows real and simulated data in the same figure or table?

By Edmund Chattoe-Brown

On one level this is a straightforward request. The earliest convincing example I have found is Hägerstrand (1965, p. 381) an article that seems to be undeservedly neglected because it is also the earliest example of a simulation I have been able to identify that demonstrates independent calibration and validation (Gilbert and Troitzsch 2005, p. 17).1

However, my attempts to find the earliest examples are motivated two more substantive issues (which may help to focus the search for earlier candidates). Firstly, what is the value of a canon (and giving due intellectual credit) for the success of ABM? The Schelling model is widely known and taught but it is not calibrated and validated. If a calibrated and validated model already existed in 1965, should it not be more widely cited? If we mostly cite a non-empirical model, might we give the impression that this is all that ABM can do? Also, failing to cite an article means that it cannot form the basis for debate. Is the Hägerstrand model in some sense “better” or “more important” than the Schelling model? This is a discussion we cannot have without awareness of the Hägerstrand model in the first place.

The second (and related) point regards the progress made by ABM and how those outside the community might judge it. Looking at ABM research now, the great majority of models appear to be non-empirical (Angus and Hassani-Mahmooei 2015, Table 5 in section 4.5). Without citations of articles like Hägerstrand (and even Clarkson and Meltzer), the non-expert reader of ABM might be led to conclude that it is too early (or too difficult) to produce such calibrated and validated models. But if this was done 50 years ago, and is not being much publicised, might we be using up our credibility as a “new” field still finding its feet?) If there are reasons for not doing, or not wanting to do, what Hägerstrand managed, let us be obliged to be clear what they are and not simply hide behind widespread neglect of such examples2.)

Notes

  1. I have excluded an even earlier example of considerable interest (Clarkson and Meltzer 1960 which also includes an attempt at calibration and validation but has never been cited in JASSS) for two reasons. Firstly, it deals with the modelling of a single agent and therefore involves no interaction. Secondly, it appears that the validation may effectively be using the “same” data as the calibration in that protocols elicited from an investment officer regarding portfolio selection are then tested against choices made by that same investment officer.
  2. And, of course, this is a vicious circle because in our increasingly pressurised academic world, people only tend to read and cite what is already cited.

References

Angus, Simon D. and Hassani-Mahmooei, Behrooz (2015) ‘“Anarchy” Reigns: A Quantitative Analysis of Agent-Based Modelling Publication Practices in JASSS, 2001-2012’, Journal of Artificial Societies and Social Simulation, 18(4), October, article 16, .

Clarkson, Geoffrey P. and Meltzer, Allan H. (1960) ‘Portfolio Selection: A Heuristic Approach, The Journal of Finance, 15(4), December, pp. 465-480.

Gilbert, Nigel and Troitzsch, Klaus G. (2005) Simulation for the Social Scientist, 2nd edition (Buckingham: Open University Press).

Hägerstrand, Torsten (1965) ‘A Monte Carlo Approach to Diffusion’, Archives Européennes de Sociologie, 6(1), May, Special Issue on Simulation in Sociology, pp. 43-67.


Chattoe-Brown, E. (2018) What is the earliest example of a social science simulation (that is nonetheless arguably an ABM) and shows real and simulated data in the same figure or table? Review of Artificial Societies and Social Simulation, 11th June 2018. https://rofasss.org/2018/06/11/ecb/