Great piece, as usual. You are right to focus on the question of asymptomatic spread and asymptomatic testing, because this issue is truly central to the perception of the pandemic. While many have written about the huge false positives that result from testing asymptomatic people in widespread screening programs, very few people, even p…
Great piece, as usual. You are right to focus on the question of asymptomatic spread and asymptomatic testing, because this issue is truly central to the perception of the pandemic. While many have written about the huge false positives that result from testing asymptomatic people in widespread screening programs, very few people, even professionals, understood exactly how big an impact this has on the perception of the pandemic. FDA wrote way back in Nov. 2020 how a 98% specific antigen test can in fact produce 96% false positives in the real world with 0.1% background prevalence of the disease at issue. And this is indeed around where we have been much of the time during the pandemic. The misperception that "Omicron" is everywhere or similar such statements is driven largely by this massive false positive rate based on asypmtomatic testing. It really is that big a part of what's happened and I urge you, Michael, to devote additional essays to this issue specifically. Here's an essay I and my colleagues wrote on this for BMJ back in June 2021: https://www.bmj.com/content/373/bmj.n1411/rr
I wonder if you could answer a question for me that's been bugging me. While I understand there must have been far too many false positives with so much testing, my own family's experience was that until we truly and noticeably caught Covid in Dec. 2021, we never had a positive test all the various times when we were sick with something else and got tested. What conditions needed to be present to cause false positives with testing?
Because for my family and people I'm close to, the covid testing didn't seem to be finding Covid when the sickness was really something else. I was worried about it because one of my children had to be tested for school if she showed any signs of sickness just to be allowed to attend for a long while, but we never had a positive test for her.
After all the confusing things we've been told these past several years, I weight my own anecdotal experiences higher than I used to simply because I know for sure they are real. I am not sure any data handed down from authorities are accurate, so anecdotal experiences of friends and family I can observe become important sources. Bottom line: I am genuinely confused about why false positives didn't happen to more people I know. It may be they did happen (in fact, I assume they did), but there was so much testing in my area and so many Covid-negative tests. I'd love your insights into what conditions would lead to inaccurate testing.
So when FDA warns about 96% false positives they mean that of those tests that are positive, 96% of them will be false positives in the 0.1% disease prevalence scenario described.
Most tests will be negative even under very high false positive scenarios. The issue is that the vast majority of test positives that do occur are false positives under screening testing that don't consider symptoms as a precondition for testing. So to be clear: most test results will still be negative but most of those that are positive will be false positives. And of course when tens of millions of tests were taking place each day in the US alone even a low rate of overall test positives will still result in a large number of false "cases," "hospitalizations" and "deaths." Does that make sense?
Great piece, as usual. You are right to focus on the question of asymptomatic spread and asymptomatic testing, because this issue is truly central to the perception of the pandemic. While many have written about the huge false positives that result from testing asymptomatic people in widespread screening programs, very few people, even professionals, understood exactly how big an impact this has on the perception of the pandemic. FDA wrote way back in Nov. 2020 how a 98% specific antigen test can in fact produce 96% false positives in the real world with 0.1% background prevalence of the disease at issue. And this is indeed around where we have been much of the time during the pandemic. The misperception that "Omicron" is everywhere or similar such statements is driven largely by this massive false positive rate based on asypmtomatic testing. It really is that big a part of what's happened and I urge you, Michael, to devote additional essays to this issue specifically. Here's an essay I and my colleagues wrote on this for BMJ back in June 2021: https://www.bmj.com/content/373/bmj.n1411/rr
And here's a more detailed article on the same issues: https://www.authorea.com/users/61793/articles/527660-the-false-positive-paradox-and-the-risks-of-testing-asymptomatic-people-for-covid-19
Thank you Tam! Exactly.
I wonder if you could answer a question for me that's been bugging me. While I understand there must have been far too many false positives with so much testing, my own family's experience was that until we truly and noticeably caught Covid in Dec. 2021, we never had a positive test all the various times when we were sick with something else and got tested. What conditions needed to be present to cause false positives with testing?
Because for my family and people I'm close to, the covid testing didn't seem to be finding Covid when the sickness was really something else. I was worried about it because one of my children had to be tested for school if she showed any signs of sickness just to be allowed to attend for a long while, but we never had a positive test for her.
After all the confusing things we've been told these past several years, I weight my own anecdotal experiences higher than I used to simply because I know for sure they are real. I am not sure any data handed down from authorities are accurate, so anecdotal experiences of friends and family I can observe become important sources. Bottom line: I am genuinely confused about why false positives didn't happen to more people I know. It may be they did happen (in fact, I assume they did), but there was so much testing in my area and so many Covid-negative tests. I'd love your insights into what conditions would lead to inaccurate testing.
So when FDA warns about 96% false positives they mean that of those tests that are positive, 96% of them will be false positives in the 0.1% disease prevalence scenario described.
Most tests will be negative even under very high false positive scenarios. The issue is that the vast majority of test positives that do occur are false positives under screening testing that don't consider symptoms as a precondition for testing. So to be clear: most test results will still be negative but most of those that are positive will be false positives. And of course when tens of millions of tests were taking place each day in the US alone even a low rate of overall test positives will still result in a large number of false "cases," "hospitalizations" and "deaths." Does that make sense?
And still today most headlines and dashboards and whatnot focus on "cases". In order to keep the idea of the pandemic alive.