Are the Coronavirus Models Too Pessimistic?

Unfortunately, if anything, reality has often turned out somewhat worse than predicted.

The White House keeps thinking that the major coronavirus models are too pessimistic and that things will turn out better than they predict.  The Administration is wrong to downplay the models’ forecasts. Rather than being too pessimistic, models have frequently erred in the direction of optimism. Despite continuing uncertainties, there’s no reason to discount their prediction downward.

Fivethirtyeight.org has a nifty feature where you can check out what some leading models were predicting as of various dates. That allows comparisons between model forecasts made at different times covering different dates. The results are instructive, as shown by the table at the end of this post.   Here are the main-takeaways.

Over-optimism by models. If anything, the models haven’t been pessimistic enough, particularly the IMHE model preferred by the White House. Predictions for deaths two weeks in the future have often turned out to be too low.  This could be an indication that social distancing has been less effective than expected or less rigorous than necessary. Or there’s something else we don’t understand about the disease.

Models are constantly tweaked. You can see that from the predicted number of deaths for April 25 made by each model ten days earlier and four days earlier.  There’s even a shift in predictions for late May between predictions made on May 1 and those made on May 5, which was quite significant for some models. (In fact, on Monday, the IMHE upped its August 4 prediction from 74,000 to 135,000).  These changes make it a little hard to know which modeling approach is better. 

There’s been notable convergence. If you compare the predictions for two weeks out (and now four weeks out), there seems to be a clear trend toward closer clustering.  Hopefully, this is a sign that learning and improved date are increasing the validity of predictions.

One more important thing to note.  All of these models have been operating under conditions where social distancing rules were in effect across the country.  As those rules are relaxed, the modelers will have to figure out how to modify the models.  Given the lag time between new infections and deaths from the disease, we probably won’t see the relaxations fully reflected in the death rates until late May. Because the amount of testing and the testing criteria are constantly shifting, it may be hard to interpret changes in the number of new cases observed.  Changes in hospitalizations will lag by a week or ten days, but may be more revealing.

The Trump Administration seems a bit adrift right now.  A recent draft report by staff does consider the possibility that things could get a lot worse.  Yet the White House also favors a home-brewed model by one of its economists that “shows deaths dropping precipitously in May — and essentially going to zero by May 15.”  The Administration needs to stop cherrypicking models and recognize the possibility that reality may end up worse, not better, than some established models predict.

Table

Key: IMHE (University of Washington model), UT (University of Texas), NE (Northeastern), Colum. (Columbia).  “Date Listed” is the date when the prediction appeared on the 538.org listing.

Date When Prediction Was Listed Deaths on Date Prediction was Listed Target Date of Prediction Predicted Number of Deaths Actual Deaths on Target Date
4/7 15K 4/11 IMHE – 21K            24K
4/14 30K 4/18 Colum. 31K

NE  36K

IMHE 34K

           39K
4/25 Colum. 51K

NE 47K

IMHE 44K

           54K
4/21 45K 4/25 Colum. 55K

NE. 55K

IMHE. 52K

UT 46K

           54K
5/16 Colum. 102K

NE 69K

IHME 66K

UT 58K

          [5/2           66K]
5/1 65K 5/2 Los Alamos 69K

Colum. 64K

NE 63K

UT 59K

IHME 62K

           66K
5/28 Los Alamos 108K

Colum. 103K

NE. 79K

UT. 74K

IHME 72K

5/5 71K 5/9 MIT 78K

IMHE 82K

Los Alamos 79K

Colum. 76K

NE 77K

UT 71K

5/30 MIT 111K

IHME 110K

Los Alamos 107K

Colum. 104 K

NE 98K

UT 93K

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About Dan

Dan Farber

Dan Farber has written and taught on environmental and constitutional law as well as about contracts, jurisprudence and legislation. Currently at Berkeley Law, he has al…

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