[exmadscientist]

> what's bullshit about temp checks?

Mostly the measurements themselves.

Internal temperature is indeed a pretty decent indicator. Yes, everyone's normal body temperature varies a bit (and thus their fever threshold), and, yes, different activities will swing your temperature around a bit, so it is sometimes tricky, but internal temperature works.

The problem is that no one measures internal temperature outside a hospital (partly because of sanitation issues). Everyone measures external -- skin -- temperature, usually using an infrared (IR) thermometer.

Those things are terrible to begin with. But they're not even used properly!

To get good results from an IR thermometer, you have to perform an emissivity correction. Which is easy enough for one measurement on one person in a lab, but it will and does vary between people by more than enough to cross the fever threshold. We've got a Flir E60 at work and have tried to use it to make this measurement reliably. We can't do it. It just isn't accurate enough. (You can get relative differences shockingly accurately, but unfortunately temperature screenings need an absolute temperature.) And that's a $10,000 IR camera, set up by skilled R&D personnel. Most places have a cheap Amazon-junk IR gun "thermometer" operated by the hapless.

Maybe we could fix that somehow, so we always get an accurate measurement of skin temperature. But, as you've probably noticed by now, skin temperature isn't internal temperature. If you, for example, walk a mile outside to reach the "temp check" station, on a chilly day... your skin will be colder than the rest of your body. Well below any fever threshold, in fact, unless your fever is so strong that you're already well aware of it (and therefore actively lying, or you'd be in some kind of quarantine by now).

So it's just not a measurement that you can make accurately enough to mean anything, at any kind of scale.

Thus, the cries of "security theater". Because it is.

I wish temperature screening worked, but it simply doesn't. Not the way it's used in practice, anyway. (And don't ask what thermal camera someone is using, because it kinda-sorta looks like the high-end one you tried out that doesn't work at all... you'll just get that good old deer-in-the-headlights look. Or worse. I was probably lucky.)

[nmfisher]

Case in point - I was stopped from entering the supermarket here in Singapore because I measured over 37 degrees Celsius....but 5 seconds later I re-measured at 32 degrees, and was waved in.

It is pretty absurd.

[ACow_Adonis]

So this comes back to my statement about proper equipment and proper thresholds.

obviously 37 practically isn't a fever, and 32 is ridiculous.

But let's accept it on face value, so it gave you a false positive, which caused you to pause for a second reading, and then a true negative (well, unless you count the 32 as a false positive for hypothermia) and you went in.

That temp checks create false readings isn't really news: for me the question is so they create statistically significantly better outcomes. As a statistics guy, my head says they do. The objections I hear to them sound to me like the objections to bmi: that it's not universally perfect is not reason to dismiss it. This seems to me like the perfect being the enemy of the good enough.

[ramraj07]

You called yourself a stats guy so I’m going to push, can you show any rigorous analysis by anyone suggesting that theres any benefit to doing temp checks? Is there any number anywhere that gives false positive rate estimates for typically used temperature checking methods? Or false negatives?

[btilly]

Here is a back of the envelope.

First of all, the important thing is the R number - how many people does the average infected person infect. If that is above 1, you get spread. Below 1, it dies out. Without mitigations, R is estimated at about 3. With mitigations, the UK is posting various numbers in the 0.7-1.0 range. (See https://www.bbc.com/news/health-52473523 for a source.) Let's assume that the USA is similar.

The question to ask is this. Do the temperature checks make the difference between being above or below 1.0?

Per https://www.webmd.com/lung/news/20210110/59-percent-of-covid... about 60% of spread comes from people who are asymptomatic. So about 40% happens from people who are symptomatic. Per https://www.healthline.com/health-news/what-is-the-risk-of-g... about 55% of spread happens at stores. If those factors were independent, about 1/4 of the spread would happen from symptomatic people at stores. If the temperature checks avoid a significant fraction of those, then in the real world it may indeed be the difference between pandemic spread and dying off.