Tag Archives: model size

Focussing on our Strengths

By Corinna Elsenbroich and Jennifer Badham

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

Understanding a situation is the precondition to make good decisions. In the extraordinary current situation of a global pandemic, the lack of consensus about a good decision path is evident in the variety of government measures in different countries, analyses of decision made and debates on how the future will look. What is also clear is how little we understand the situation and the impact of policy choices. We are faced with the complexity of social systems, our ability to only ever partially understand them and the political pressure to make decisions on partial information.

The JASSS call to arms (Flaminio & al. 2020) is pointing out the necessity for the ABM modelling community to produce relevant models for this kind of emergency situation. Whilst we wholly agree with the sentiment that ABM modelling can contribute to the debate and decision making, we would like to also point out some of the potential pitfalls inherent in a false application and interpretation for ABM.

  1. Small change, big difference: Given the complexity of the real world, there will be aspects that are better and some that are less well understood. Trying to produce a very large model encompassing several different aspects might be counter-productive as we will mix together well understood aspects with highly hypothetical knowledge. It might be better to have different, smaller models – on the epidemic, the economy, human behaviour etc. each of which can be taken with its own level of validation and veracity and be developed by modellers with subject matter understanding, theoretical knowledge and familiarity with relevant data.
  2. Carving up complex systems: If separate models are developed, then we are necessarily making decisions about the boundaries of our models. For a complex system any carving up can separate interactions that are important, for example the way in which fear of the epidemic can drive protective behaviour thereby reducing contacts and limiting the spread. While it is tempting to think that a “bigger model”, a more encompassing one, is necessarily a better carving up of the system because it eliminates these boundaries, in fact it simply moves them inside the model and hides them.
  3. Policy decisions are moral decisions: The decision of what is the right course to take is a decision for the policy maker with all the competing interests and interdependencies of different aspects of the situation in mind. Scientists are there to provide the best information for the understanding of a situation, and models can be used to understand consequences of different courses of action and the uncertainties associated with that action. Models can be used to inform policy decisions but they must not obfuscate that it is a moral choice that has to be made.
  4. Delaying a decision is making a decision to do nothing: Like any other policy option, a decision to maintain the status quo while gathering further information has its own consequences. The Call to Action (paragraph 1.6) refers to public pressure for immediate responses, but this underplays the pressure arising from other sources. It is important to recognise the logical fallacy: “We must do something. This is something. Therefore we must do this.” However, if there are options available that are clearly better than doing nothing, then it is equally illogical to do nothing.

Instead of trying to compete with existing epidemiological models, ABM could focus on the things it is really good at:

  1. Understanding uncertainty in complex systems resulting from heterogeneity, social influence, and feedback. For the case at hand this means not to build another model of the epidemic spread – there are excellent SEIR models doing that – but to explore how the effect of heterogeneity in the infected population (such as in contact patterns or personal behavior in response to infection) can influence the spread. Other possibilities include social effects such as how fear might spread and influence behaviours of panic buying or compliance with the lockdown.
  2. Build models for the pieces that are missing and couple these to the pieces that exist, thereby enriching the debate about the consequences of policy options by making those connections clear.
  3. Visualise and communicate difficult to understand and counterintuitive developments. Right now people are struggling to understand exponential growth, the dynamics of social distancing, the consequences of an overwhelmed health system, and the delays between actions and their consequences. It is well established that such fundamentals of systems thinking are difficult (Booth Sweeney and Sterman https://doi.org/10.1002/sdr.198). Models such as the simple models in the Washington Post or less abstract ones like the routine day activity one from Vermeulen et al (2020) do a wonderful job at this, allowing people to understand how their individual behaviour will contribute to the spread or containment of a pandemic.
  4. Highlight missing data and inform future collection. This unfolding pandemic is defined through the constant assessment using highly compromised data, i.e. infection rates in countries are entirely determined by how much is tested. The most comparable might be the rates of death but even there we have reporting delays and omissions. Trying to build models is one way to identify what needs to be known to properly evaluate consequences of policy options.

The problem we are faced with in this pandemic is one of complexity, not one of ABM, and we must ensure we are honouring the complexity rather than just paying lip service to it. We agree that model transparency, open data collection and interdisciplinary research are important, and want to ensure that all scientific knowledge is used in the best possible way to ensure a positive outcome of this global crisis.

But it is also important to consider the comparative advantage of agent-based modellers. Yes, we have considerable commitment to, and expertise in, open code and data. But so do many other disciplines. Health information is routinely collected in national surveys and administrative datasets, and governments have a great deal of established expertise in health data management. Of course, our individual skills in coding models, data visualisation, and relevant theoretical knowledge can be offered to individual projects as required. But we believe our institutional response should focus on activities where other disciplines are less well equipped, applying systems thinking to understand and communicate the consequences of uncertainty and complexity.


Squazzoni, F., Polhill, J. G., Edmonds, B., Ahrweiler, P. , Antosz, P., Scholz, G., Chappin, E., Borit, M., Verhagen, H., Francesca, G. and Gilbert, N. (2020) Computational Models That Matter During a Global Pandemic Outbreak: A Call to Action. Journal of Artificial Societies and Social Simulation 23(2), 10. <http://jasss.soc.surrey.ac.uk/23/2/10.html>. doi: 10.18564/jasss.4298

Booth Sweeney, L., & Sterman, J. D. (2000). Bathtub dynamics: initial results of a systems thinking inventory. System Dynamics Review: The Journal of the System Dynamics Society, 16(4), 249-286.

Stevens, H. (2020) Why outbreaks like coronavirus spread exponentially, and how to “flatten the curve”. Washington Post, 14th of March 2020. (accessed 11th April 2020) https://www.washingtonpost.com/graphics/2020/world/corona-simulator/

Vermeulen, B.,  Pyka, A. and Müller, M. (2020) An agent-based policy laboratory for COVID-19 containment strategies, (accessed 11th April 2020) https://inno.uni-hohenheim.de/corona-modell

Elsenbroich, C. and Badham, J. (2020) Focussing on our Strengths. Review of Artificial Societies and Social Simulation, 12th April 2020. https://rofasss.org/2020/04/12/focussing-on-our-strengths/