New York coronavirus antibody study: Why I had nothing to say to the press on this one.

The following came in the email:

I’m a reporter for **, and am looking for comment on the stats Gov Cuomo just released. Would you be available for a 10-minute phone conversation? Please let me know.

Thanks so much, and here’s the info:

Here is the relevant part:

In New York City, about 21 percent, or one of every five residents, tested positive for coronavirus antibodies during the state survey. The rate was 16.7 percent in Long Island, 11.7 percent in Westchester and Rockland Counties, and 3.6 percent in the rest of the state.

Almost 14 percent of those tested in New York were positive, according to preliminary results from the state survey, which sampled approximately 3,000 people over two days at grocery and big-box stores.

I spoke with the reporter for a few minutes and gave my quick take:

– Those California studies estimating 2% or 4% infection rate were hard to assess because of the false-positive problem: if a test has a false positive rate of 1% and you observe 1.5% positive tests, your estimate’s gonna be super noisy. But if 20% of the tests you observe are positive, then the false-positive rate is less of a big deal.

– That said, I know nothing about how the tests were done. I have no idea what exactly it’s measuring or what its error rates are.

– Also, is 21% the raw proportion of positive tests, or has the number been adjusted for false positive and negative rates?

– In any case, the 20% number seems reasonable. It’s hard for me to imagine it’s a lot higher, and, given the number of deaths we’ve seen already, I guess it can’t be much lower either.

– I can’t figure out if doing a survey at grocery and big-box stores will overestimate or underestimate the infection rate. On one hand, people who are going out to the store could be at higher risk for exposure. On the other hand, sick people would be staying at home, right? But, then again, think of all the uninfected people holing up and never going out . . . And where exactly were these stores? I keep going in circles on this one.

– In any case, this sort of survey is a good thing. We keep doing surveys in different ways, each survey has its own bias, put them all together and we’ll learn some things.

After 10 minutes I’d spewed out enough material for as many quotes as the reporter could possibly have wanted from me.

But then I got off the phone and started thinking . . . Do I want to be quoted as saying this estimate is pretty good? Or that it’s flawed? I don’t know. There’s no data, no report. Based on the news report, the study seems to have been conducted by the state health department, and that sounds like a good sign. In general I’ll have more trust in a study from the state health department than from some Stanford professors. I’m not joking here: the health department are professionals and they don’t have the same incentives that academics have to hype their research. But, still, I have no idea what’s going on.

So I sent an email to the reporter:

Hi—just thinking more about this, I’d prefer if you not quote me in this article. I make this request because I don’t think I have anything particular to add here, and it would be better for you to quote an expert, or to not have a quote at all. I have not seen the data or even any report undelying the claims from this New York State study, so I can’t really make any reasonable statements.
Thanks for understanding.

There was more to say about those California studies because (a) the people who did those studies released some partial information, (b) the thing about the false-positive rate mentioned above, and (c) the people involved made a bunch of loud and weakly-supported claims. This new study is more of an official number, so there’s not much that can be said from a statistical perspective until the results are unpacked in some way.