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ERGODICITY AND THE PANDEMIC
Inspired by the quoted tweet below, let's see other failures of failing to understand (non-)ergodicity in this pandemic
(thread; 1/N) https://twitter.com/ole_b_peters/status/1245383951377674241?s=20
Inspired by the quoted tweet below, let's see other failures of failing to understand (non-)ergodicity in this pandemic
(thread; 1/N) https://twitter.com/ole_b_peters/status/1245383951377674241?s=20
2/ First, a definition of ergodicity in the image below.
3/ Considering the average number of ICU beds or the percentage of infected in a nation is a failure of understanding (non-)ergodicity.
Having 10k cases across a large country allows to attend to all of them; having 10k cases in a province collapses the healthcare system.
Having 10k cases across a large country allows to attend to all of them; having 10k cases in a province collapses the healthcare system.
4/ Using average mortality rates is another failure of understanding ergodicity.
Mortality rate is not a universal constant; it depends on healthcare system saturation and other variables.
It is path dependent, thus non-ergodic, thus non-averageable.
Mortality rate is not a universal constant; it depends on healthcare system saturation and other variables.
It is path dependent, thus non-ergodic, thus non-averageable.
5/ Here is another example: https://twitter.com/rorysutherland/status/1245922761244954630?s=20
6/ Small forecast ranges like those in the chart below are idiotic because number of cases is a path-dependent variable under multiplicative dynamics: it *will* have very different outcomes in parallel words due to small variations in the initial path. https://twitter.com/ngriffin360/status/1245092358024130560?s=20
7/ Studies which attempt to simulate the diffusion of the virus in a country using an average R0 are similarly completely ignoring any form of path-dependence.
8/ Another problem of many COVID models: they assume an ergodic population. https://twitter.com/TaylorPearsonMe/status/1247651374550130690?s=20
9/ Another example in which ergodicity is wrongfully assumed related to the pandemic:
an index which "mostly recovered" (GDP, S&P, Dow, etc.) does not imply – not at all – that the economy "recovered for most people".
an index which "mostly recovered" (GDP, S&P, Dow, etc.) does not imply – not at all – that the economy "recovered for most people".
10/
https://twitter.com/naval/status/1258934104550019072?s=21 https://twitter.com/naval/status/1258934104550019072
https://twitter.com/naval/status/1258934104550019072?s=21 https://twitter.com/naval/status/1258934104550019072
11/ What happens in the long run matters only if we can get there. https://twitter.com/CT_Bergstrom/status/1242321919233277952?s=20
