I’ve spent the last few days picking through Neil Ferguson’s Covid model.
It contains 450 different parameters, each of which is either a single float or a float matrix. The majority of these are not based on any ground truth data that I can see and are just… … “magic numbers” presented in the model. Any one of them can change the outputs of the model in unpredictable ways.
The model is essentially a giant, complex state machine. Its stochastic, which basically just means its contains random elements – so the no two runs… … produce the same results.
The code itself contains many special rules held in imperative C++. There is no explanation as to why these are present. For example, why are hotel’s excluded in the “place sweep”? Who knows, but they are.
The complexity is hence… …Cartesian product of the input parameters and the embedded code rules.
All this wouldn’t matter if it delivered reasonable results. However, no amount of fiddling with parameters deliver Swedish deaths of less than 90k. The model just consistently over counts infected and… … hence dead.
I am not even going to go into the bugs that are listed in the issues list. Some of which results in +/- 80k deaths.
All in all, this is not a clear, transparent model, based on firm ground truth data. Its a fairly arbitrary Heath Robinson machine, which over counts infections on a consistent basis. Thanks all for your responses, questions and challenges. Too many to respond to them all I’m afraid. But all will be read. Strange that many academics have jumped in with “get off my land” style comments. This is such a thread. Worth a read.
Sample of parameters for which arbitrary inputs are included:
This is the model that broke the global economy….