2020-07-07 – Right-wing media are trumpeting a declining death rate as evidence that the pandemic is over-ish. Is a declining death rate good news? Can we stop our precautions (such as they are)?

Of course a declining death rate is good news. (They want to make us out to be ghouls, saying that we wouldn’t cheer a declining death rate. We absolutely cheer a declining death rate.)

But here’s the problem: the number of deaths (we’re talking actual dead people, not percentages)—the number of deaths is the product of two numbers: the number of cases and the disease’s lethality. So let’s look at some hypothetical figures (simplified for purposes of illustration):

Let’s say the lethality figure is 0.5% and we have 100,000 cases. We would expect 500 dead.

But let’s say that (for some reason) the lethality figure drops to 0.2%. Out of 100,000 cases we would expect 200 dead. I’d call that good news. It’s not as good as zero dead, but it’s better than 500 dead.

But let’s say that we rejoice over the drop in lethality and stop taking precautions and the number of cases soar to 250,000. Even though we are fortunate to have reduced lethality to 0.2%, the increased number of cases now comes to the same 500 we had when the lethality figure was 0.5% (with 100,000).

And remember, even if we keep the number of cases steady (which is not happening), we still have 200 dead out of this 100,000 population.

Multiply this by a lot to extend this example to the entire US population. (Caveat: it is unlikely that the number of cases would increase by the exact inverse of the drop in lethality that I am showing in my example. I just wanted to illustrate the principle.)

So, it is good news that the lethality of the disease may be dropping, but it is far, far, far from reason to stop wearing your mask.

(Why may the lethality rate be dropping? It may not be dropping. It is more likely that this rate would drop as data gets better than that it would rise because the number of dead is less uncertain than the number of cases. Or—it may be dropping because doctors are finding better ways of treating people. That is likely. Or—it may be dropping because less-lethal strains of COVID are spreading faster than more-lethal strains. This is also likely. All of these factors are probably at work.)

So, to sum it all up: Sure, a declining death rate is great news. If it’s happening. And if we are not engaging in risky behavior because we thing we’re all clear.

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