Tuesday, July 21, 2020

Pretending that Good News is Bad News

The headline of a news story today:

CDC study shows COVID-19 cases may be 10 times higher than reported

The story warns that this shows that states that are opening up are making a mistake, that the problem is worse than we thought. It does not seem to have occurred to the author that if there are ten times as many cases as we thought and the same number of deaths, that means that the disease is only a tenth as lethal as we thought it was, which is an argument in favor of opening up, not against. Nobody has been arguing that we should respond to each year's flu season with a lockdown.

The article also does not mention that this is the same result, in a somewhat stronger form, that was reported by people at Stanford quite a while back, on a similar basis, and for which they were severely criticized.

The explanation may be political bias. Trump has tended to downplay the seriousness of Covid, his opponents to do the opposite, and most reporters, probably including the author of this article, are opposed to Trump. But it may also be the bias that leads many people to believe that everyone else should be taking more precautions — against Covid, overweight, or anything else — than they are, hence to regard it as socially responsible to exaggerate any news that makes a threat look bigger, downplay or ignore news that makes it look smaller.

It is an issue I have discussed before, in other contexts, several times.

P.S. Looking at another source, it looks as though the claim is between two and thirteen times the number of known cases (for the U.S.). But I think previous mortality estimates already took account of some asymptomatic cases, so were using something larger than the known cases figure.

That said, the commentary continues to get precisely the wrong conclusion:

Jennifer Nuzzo, an epidemiologist at the John Hopkins Center for Health Security who was uninvolved in the study, told The Washington Post. “This study should put to bed any further argument that we should allow this virus to rip through our communities in order to achieve herd immunity.”

If the number of people who have had the virus is (say) twice the number we thought it was, then the deaths we have suffered so far have brought us twice as far towards herd immunity as we thought. Aiming at herd immunity may or may not make sense, but the new evidence makes the strategy look better than before, not worse, which is the opposite of Ms Nuzzo's claim.


Ricardo Cruz said...

I am not sure this necessarily reflects anti-Trump bias because the same thing is true in my country and - from what I can tell - pretty much of the entire world. I just think readers go after the gloom and doom stories and journalists respond accordingly. For example, a lot of coverage on covid reported asymptomatic infected as being also potential carriers as if this was something new in respiratory diseases. Many other things were reported as unique of sars-cov-2, but which are actually transversal to other coronaviruses (like the lower immunity time) and even other pathogens. I think the media now has competition from social media platforms and so needs to be more and more outrageous to capture eyeballs.

Oskar Mathiasen said...

So i do not believe this is what the reporter did, but there is a way this data, even if it increases your expectation of number of infected, can decrease the probability herd immunity is the right strategy.

It could be that you before reading you believed that you had to have 20 (picked arbitrarily, any number above 13 would work) times as many cases as reported for herd immunity to be the optimal strategy.

Then this data could make you update your priors, resulting in a posterior with the following 2 properties.
1. the expectation of the number of infected is higher for the posterior than the prior
2. the probability that the number of infected is above 20 times the reported numbers is lower according to the posterior compared to the prior.

Again it is rather unlikely this is what the article actually did, more an interesting idea to keep in mind.

missprism said...

I tried to post this blog post to Twitter. It wouldn't let me. I wonder what that is about.

Anonymous said...

If you're reopening because you don't think that the disease is very harmful or because you think it's hopeless to prevent an outbreak, then learning that it's more widespread is pretty much good news.

But if you're reopening because you think you know how to be careful to prevent an outbreak, then learning that it's more widespread is bad news.

Alan said...

Are you assuming that death, sometime within the first few months after infection, is the only bad outcome that matters? We don't know that at all. It's a weird, nasty, unpredictable, poorly understood virus. Never getting infected is strongly preferable to getting infected, even if you have no obvious symptoms.