Analysis of the Imperial College Epidemiological Model
This is not really a great analysis. I would like to see an analysis from someone who:<p>-Is actually familiar with academic code so that the usual pearl clutching can be tempered with realism. That doesn&#x27;t mean throwing up one&#x27;s hands and just accepting that all academic code is like this, but it does mean coming from a place of knowing what normal academic code looks like (much worse than this).<p>-Is actually familiar with production forecasting in other contexts (outside of the small bubble of SV) the writer says they have &quot;done some model review of financial models&quot;. I have done a lot of such reviews and many models are implemented in idiosyncratic Excel. Yes, models that drive policy decisions in government and large transactions in finance, models that are used in internal forecasting in many places. All Excel.<p>A recognition of the difference between should and is. There are claims here about what should be done in modelling which are correct but with little recognition that they almost never are.<p>Really I would like to see a review by someone who is familiar enough with epi modelling <i>and</i> with modern software engineering practices to give a balanced assessment.<p>The only material criticism of the model that isn&#x27;t just &quot;this should have been implemented better&quot; is that it assumes that people will not voluntarily implement forms of social distancing when many people are dying and that this distorts upwards the death count. An agent based model would model people&#x27;s time varying contact matrices based on what they can observe (so as death rates go up, voluntary social distancing goes up as well).<p>Presumably this leads to a higher peak than mandatory measures because deaths lag measures which are visible to policy makers but not to the public, therefore people will distance later.<p>This is indeed not addressed in the model. It could be addressed exogenously by making interactions dependent on the rolling average death count of the last several days as that is probably the signal that will the cause the most widespread panic.<p>However. There is some important context here which is that:<p>-This was not even the only model used by SAGE. The LSHTM model was run alongside it and gave similar results.<p>-The &quot;no intervention&quot; case was sense checked using the basic equations of epidemiology.<p>Models that drive decisions can be criticised on technical-procedural grounds (ideally this model should use fewer globals, and use psuedorandomness better so that it gives the exact same result on every run rather than more-or-less the same result on every run) and on model concept basis (the model assumes zombies) but the most important assessment of real models is how they drive decisions.<p>In that regard the model was successful and drove the same decision as the very different LSHTM model, the models used by almost every other country, and what could be estimated using Epi 101.<p>That is the necessity of mass social distancing. Even the Swedes, incidentally, accept this. They have chosen to make everything except for the closure of the highest risk establishments voluntary. I wonder though if isn&#x27;t the case that these restrictions are in practice voluntary in many cases even in the UK. I could easily visit my family and friends - the police would never know. My employer could continue having us come into work - there is no absolute ban on office workers being required to come in, just guidance that people who can work from home should. The actual legislation can be considered not only as enforceable rules but also as high-cost signalling. There will be people who simply will not take it seriously otherwise on the grounds that &quot;if it were really that bad, they would ban it&quot;<p>So to come back to the one substantive criticism - what different advice would a model that implemented behaviour changes have led to? I don&#x27;t think it would have changed anything, if you tell policymakers: &quot;listen, we don&#x27;t necessarily need to make these things mandatory, once the coffins pile up people will stay home by themselves&quot; what do you think that is going to drive? They&#x27;re hardly likely to decide that we can leave off the restrictions. We came up to 80% or so of ICU capacity as it was. That tells me that anything that led to less or later social distancing would have put us in the position that Bergamo or Madrid were - at least localised and temporary overwhelming of hospitals. Potentially much worse.