Gary Robinson's Rants

COVID-19 Prediction Update

[A note on these predictions: the following is a coldly analytical look at fatalities counts. Every single death is an enormous personal tragedy to the families, friends, and associates of the person who died, and such an analysis seems to completely ignores that fact. And yet, only by such pure analysis can we gain the tools needed to successfully fight the virus and reduce, and finally end, the tragedies. And that should be our goal. Accordingly, here we take a bit of time to take a hard look at the numbers.]

 

As of April 24, the Institute for Health Metrics and Evaluation is predicting  67,641 US COVID-19 deaths by August 4, 2020.[1]  Their prediction for August 4 has been varying quite a bit; the prediction for that date made on April 12 was  61,545, and it was 60,308 on April 19. It does seem that their predictions are rising,  bringing them a bit more in line with my Stupid Simple Model (SSM).

Essentially, this is a contest between the SSM and the IHME’s predictions that were made on April 12. On April 12, the IHME predicted 61,545 deaths by Aug 4. And on that same day, the SSM predicted more fatalities than that by April 22. It’s now past April 22, so the SSM was wrong. However, it still appears that it may turn out to be _much_more correct than the IHME.

 

See [2] for a description of the theoretical basis of the SSM.

While the contest is to see whose predictions for August 4 that were made on April 12 were more correct, both models are still being updated. Today, the SSM is predicting almost exactly  61,545 deaths (specifically, 61,493) on April 26, just 2 days from now.

Below is the recent growth in fatality rates. It depicts the multiplicative factor by which one day’s count of fatalities was more than the day before's:


2020-04-01: 1.24
2020-04-02: 1.26
2020-04-03: 1.18
2020-04-04: 1.13
2020-04-05: 1.13
2020-04-06: 1.14
2020-04-07: 1.19
2020-04-08: 1.15
2020-04-09: 1.13
2020-04-10: 1.12
2020-04-11: 1.1
2020-04-12: 1.08
2020-04-13: 1.07
2020-04-14: 1.1
2020-04-15: 1.1
2020-04-16: 1.16
2020-04-17: 1.12
2020-04-18: 1.05
2020-04-19: 1.05
2020-04-20: 1.04
2020-04-21: 1.06
2020-04-22: 1.05
2020-04-23: 1.07

For the SSM, we average the last 8 days’ exponential growth and get 1.0742. We then take yesterday’s numbers:

2020-04-23: Deaths: 3,329; Accumulated deaths: 49,951

Finally, we project forward using that rate of exponential growth applied daily:

2020-04-24: Increase: 3,575 Total: 53,526
2020-04-25: Increase: 3,841 Total: 57,368
2020-04-26: Increase: 4,125 Total: 61,493
2020-04-27: Increase: 4,431 Total: 65,925
2020-04-28: Increase: 4,760 Total: 70,686
2020-04-29: Increase: 5,113 Total: 75,800
2020-04-30: Increase: 5,493 Total: 81,293
2020-05-01: Increase: 5,900 Total: 87,193
2020-05-02: Increase: 6,338 Total: 93,531
2020-05-03: Increase: 6,808 Total: 100,340
2020-05-04: Increase: 7,313 Total: 107,653
2020-05-05: Increase: 7,855 Total: 115,508
2020-05-06: Increase: 8,438 Total: 123,946
2020-05-07: Increase: 9,063 Total: 133,010[1] https://covid19.healthdata.org/united-states-of-america

 

[2] The idea behind the SSM is that models like that IHME are too attached to details of the current situation that are very likely not reflective of the long-term situation. Since we don’t know the truth of what is going to happen tomorrow, we don’t really know whether the day-to-day multiplicative increase in fatalities is going to be greater or smaller than it is now. Since we don’t now which way it will go, we consider it to be safest to assume it will remain the same. We are therefore considering no data whatsoever beyond the daily published fatality counts. They may go down as social distancing has more of an effect, or they may go up because deaths that were classified as due to other illnesses get reclassified as due to COVID-19, or because there is a big protest in Kentucky where many people become infected. We just don’t know what will happen. So, according to the SSM, the most reasonable estimate is that growth will be similar to what we’ve been recently experiencing, since that estimate is in the center of the range of possibilities.

The Stupid-Simple Model still appears to be beating the IMHE

[Update: This blog contained a series of posts showing the results of my Stupid Simple Model for predicting the number of covid fatalities. I deleted most of them because they're irrelevant now. But the upshot is that the SSM was more accurate than the IHME. The philosophy of the SSM was that the IHME was trying to make predictions based on a number of factors that we just didn't know enough about to be meaningful. From the SSM's perspective, they were therefore just noise, more likely to cause distortions than be helpful, and a better prediction could be made by simply extending overall statistical trends. That is, we assume that, while there is a broad range of potential outcomes, the trends have already seen are at the center of those possibilities. That turned out to be more reliable basis for predicting than assuming that we could make use of  truckloads of factors we didn't actually understand. In the end, up to the date for which the SSM had made predictions, it was more accurate than the IHME. ]

 

As of April 17, the Institute for Health Metrics and Evaluation is predicting  60,308 US COVID-19 deaths by August 4, 2020.[1]  (Down from their  prediction of 68,841 yesterday, and from a prediction 61,545 for that date made on April 12.)

Essentially, this is a contest between the Stupid-Simple  Model (SSM) and the IHME. On April 12, the IHME predicted 61,545 deaths by Aug 4. And on that same day, the SSM predicted more fatalities than that by April 22. And it’s still predicting that. That’s 4 days from now! Who will turn out to be closer to correct? 


Below is the recent growth in fatality rates:


2020-04-01: 1.24
2020-04-02: 1.26
2020-04-03: 1.18
2020-04-04: 1.13
2020-04-05: 1.13
2020-04-06: 1.14
2020-04-07: 1.18
2020-04-08: 1.16
2020-04-09: 1.12
2020-04-10: 1.13
2020-04-11: 1.1
2020-04-12: 1.08
2020-04-13: 1.07
2020-04-14: 1.1
2020-04-15: 1.1
2020-04-16: 1.16
2020-04-17: 1.12

For the SSM, I  average the last 8 days’ exponential growth and get 1.1059. We then take yesterday’s numbers:

2020-04-17: Deaths: 3,857; Accumulated deaths: 36,773

Finally, we project forward using the SSM, seeing that the SSM anticipates more fatalities  by 4 days from now (Apr 22) than the IHME predicts for Aug 4. 

2020-04-18: Increase: 4,265 Total: 41,038
2020-04-19: Increase: 4,717 Total: 45,755
2020-04-20: Increase: 5,217 Total: 50,972
2020-04-21: Increase: 5,769 Total: 56,742
2020-04-22: Increase: 6,380 Total: 63,123
2020-04-23: Increase: 7,056 Total: 70,179
2020-04-24: Increase: 7,804 Total: 77,984
2020-04-25: Increase: 8,630 Total: 86,614
2020-04-26: Increase: 9,544 Total: 96,159
2020-04-27: Increase: 10,555 Total: 106,715
2020-04-28: Increase: 11,674 Total: 118,389
2020-04-29: Increase: 12,910 Total: 131,300
2020-04-30: Increase: 14,278 Total: 145,578
2020-05-01: Increase: 15,790 Total: 161,368

[1] https://covid19.healthdata.org/united-states-of-america

COVID-19 prediction

[I will be updating this daily for the foreseeable future.]

A very simple,  two-week-ahead COVID-19 fatalities  predictor. The main purpose of this predictor is to give a better sense of the implications of  exponential growth to viewers who may not have a strong intuitive sense of that. Also, it’s for people like me who simply want to know: “If conditions stay as they are, where will we be in two weeks?” Finally, if it spurs discussion about the causes for changes in the exponential growth factors, that would be great too.

Daily change in exponential growth factors:
2020-03-27: 1.31
2020-03-28: 1.28
2020-03-29: 1.22
2020-03-30: 1.21
2020-03-31: 1.3
2020-04-01: 1.23
2020-04-02: 1.25
2020-04-03: 1.2
2020-04-04: 1.19
2020-04-05: 1.14

COMMENTARY: 
The most recent exponential growth rate is the lowest yet. This may indicate a temporary slowdown, or a long-term one. Perhaps it’s driven by the slowdown in NYC.  Deaths in NYC for Saturday, Sunday, and Monday were 630, 599, and 594, respectively. That slowdown is probably because of the high level of social distancing occurring there. Without it, the rates would have been much higher even if there were  an infinite supply of hospital beds on ventilators,  but there aren’t, so the death rates would  have been even higher. 

Yesterday’s US fatalities: 9,616

Predicted total  fatalities for the US based on the average growth rate for the most  recent 3 days:
2020-04-06: 11,303
2020-04-07: 13,287
2020-04-08: 15,620
2020-04-09: 18,361
2020-04-10: 21,584
2020-04-11: 25,373
2020-04-12: 29,827
2020-04-13: 35,062
2020-04-14: 41,216
2020-04-15: 48,451
2020-04-16: 56,955
2020-04-17: 66,952
2020-04-18: 78,704
2020-04-19: 92,518

COMMENTARY: Yesterday’s model predicted a total of 120,378 on 4/18. So today’s 78,704 is quite a change for that  date, showing the power of relatively small changes  to an exponential growth rate. Let’s hope the  growth rate continues getting  smaller.