The last couple of posts outlined a number of examples of why COVID testing is important, and spelled out how easily the statistical end of any testing program can become problematic. Unfortunately, there are even more ways in which things can go wrong. In one of his articles, writer and editor Nate Silver mentioned the false-negative test result, which in the early days accounted for around 30% of tests administered. In other words, about one person in three whose test came out negative was actually infected.
The word on false positives is more encouraging. Some very meticulous research was done in Iceland, where large numbers of people were tested whether they experienced any symptoms or not. In this testing of the population at large, the false-positive results amounted to less than 1%.
Silver runs through the various assumptions under which people labor, concerning the numbers of tests conducted, and who is chosen to be tested, and so forth. Timing is a significant factor, because…
[…] a 15-day delay between when someone gets infected and when their case shows up in the data as a positive test makes a huge difference. Even if everything else was going perfectly […] a 15-day delay would result in there being about 18 times more newly infected people in the population than the number of newly reported positive tests at any given time… [I]t still means we’re always looking two weeks into the past whenever “new” data is reported.
We will be looking at other problems the author described, but for now, the bottom line is that testing the general population, whether symptomatic or not, is vitally important if the statisticians and other scientists are to form an accurate picture of what is really going on. Since the vaccines have been available, and some people have now been vaccinated for many months, a new issue in this area is the breakthrough cases.
I can’t hear you!
According to epidemiologist Dr. Eric Feigl-Ding,
Breakthrough infections are those in which the SARS-CoV-2 RNA is detected in a person who has been fully vaccinated. [W]hat we still don’t have a good handle on is breakthrough infections. These require contact tracing, which is hard to do in super-spreading events. Finding the index patient is not an easy matter.
A cliché of visual humor is the person who refuses to listen to something they don’t want to hear. This is accomplished by plugging the ears and loudly repeating “la-la-la-la-la-la,” ad infinitum. The possibilities include closed eyes, a defiant stare at the speaker, or the abstracted, off-to-the-side option.
In May of this year, the Centers for Disease Control stopped tracking breakthrough cases. La-la-la-la-la-la.
Your responses and feedback are welcome!
Source: “Coronavirus Case Counts Are Meaningless,” FiveThirtyEight.com, 04/04/21
Source: “Epidemiologist Eric Feigl-Ding calls CDC’s mask reversal a ‘mess’,” WSWS.org, 05/21/21
Image by oddharmonic/CC BY-SA 2.0