Monday, April 13, 2020

A reply to Tyler Cown's questions on Epidemiology

This is Joseph.

Tyler Cowen had a critique of epidemiological disease models. Based on the list of issues, I think he is critiquing the IHME model, which is a medicine unit led by a trained DPhil Economist (Chris Murray) and which is more of a Health Economics unit than an epidemiology one (happy to correct if Tyler wants to link to some Epidemiology models). But the big Epidemiology models are the ones from Imperial College and the critiques seem misplaced for those models. But this is, of course, a guess.

But he asked some questions and so here are some answers

a. As a class of scientists, how much are epidemiologists paid?  Is good or bad news better for their salaries?

Epidemiologists are typically paid above average for academics, because of their links to medical schools. Those in departments of public health are shamefully underpaid. Since people want good news from them, there is some pressure to produce good news and most of our scandals come from over-optimistic forecasts.

b. How smart are they?  What are their average GRE scores?

Very hard to answer as there is no undergraduate preparation. So the field contains a lot of MDs (no GRE scores) and people from a diverse set of backgrounds. I would say that the variance is high, more than anything else.

c. Are they hired into thick, liquid academic and institutional markets?  And how meritocratic are those markets?

They are often hired into soft money positions that are contingent on grant funding. I was in one such for about a decade. This is a selection process that breeds productivity, although a lot of it is in the area of grant writing.

d. What is their overall track record on predictions, whether before or during this crisis?

Very little of Epidemiology in in forecasting. I am an infectious disease epidemiologist and generally do not do epidemic forecast models. I look at treatment effectiveness.

e. On average, what is the political orientation of epidemiologists?  And compared to other academics?  Which social welfare function do they use when they make non-trivial recommendations?

Public health, as a field, tends to rely on efficient government. It is no more odd to see epidemiologists as left leaning then it would be to see a small business trade association president as right leaning. I think it was Megan McArdle who pointed out that the best model of government being effective is public health (vaccinations, public sanitation, etc . . .)

f. We know, from economics, that if you are a French economist, being a Frenchman predicts your political views better than does being an economist (there is an old MR post on this somewhere).  Is there a comparable phenomenon in epidemiology?

There are huge wars in Epidemiology but they are not driven by country so far as I can tell. It's more by epidemiological sub-field. Observational versus experimental. Causal inference versus traditional epidemiology. That sort of thing.

g. How well do they understand how to model uncertainty of forecasts, relative to say what a top econometrician would know?

In my experience, very. Look at the range of forecasts in the Imperial College models which are far greater then the IHME model. They do better than 10-fold differences in forecasts based on the response functions of the government and populace.

h. Are there “zombie epidemiologists” in the manner that Paul Krugman charges there are “zombie economists”?  If so, what do you have to do to earn that designation?  And are the zombies sometimes right, or right on some issues?  How meta-rational are those who allege zombie-ism?

Some fields of epidemiology have simply no high quality data (see nutritional epidemiology); fields with access to robust experiments tend to purge these ideas. Again, part of the problem is the variance in both people and subjects in "epidemiology" is huge, as are the tools available. Fields with experiments definitely kill off Zombie ideas, less so when it is all observational.

i. How many of them have studied Philip Tetlock’s work on forecasting?

I know of it, and tend to think that it is less applicable for disease models which tend to be more mechanistic. But epidemic curves are not my sub-field. That said we have had some incredible blunders in epidemiology (Farr's Law) when we get too mechanistic.


  1. Awesome response, Joseph! I'm a civil engineer working in public health, specifically water/wastewater design, but also working in the "paper water problems" of water rights and other legal frameworks that govern water use in the western states. I have a lot of economist and epidemiologist envy as two paths not taken. I enjoyed your thoughts!

  2. Economist here linked to your blog marginal revolution. Thanks for your thoughtful answers. Been encouraging my oldest daughter to consider epidemiology. Sounds like an MD with infectious disease focus and an MPH may be the optimal path if you can swing it.

  3. Thank you!
    That at least one epidemiologist is willing and able to answer questions / criticism rather than dismiss them out of hand raises my opinion of the field (and of blogs over Twitter)

  4. Thank you for the thoughtful answers to important questions.

  5. Thank you for the response and TC for the questions.

  6. I'm not sure Tetlock's model is the way to go in forecasting. Good on continuous phenomena, not so good on discontinuous - like his superforecaster prediction of the Brexit vote, giving Brexit a 23% chance of happening., or his pretty not very good predictions of how many Coronavirus cases there were going to be.