Comment by bananapear | Hacker News Reader

Comment by bananapear | Hacker News Reader

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At least in this case a false positive is unlikely to have any negative effects other than temporary anxiety while awaiting further screening, which is vastly more preferable to a false negative.

The use of COVID PCR tests for "mass testing" of asymptomatic individuals in the UK has resulted in the number of positive "cases" corelating more closely with the number of tests performed than with other measures[1], such as the number of people in hospital or dying with respiratory symptoms. This has been used to justify more extreme lockdown measures.

There have been estimates of the false positive rate[2] but it is likely to vary widely as the tests are administered by untrained personnel and not stored according to the manufacturer's recommendations. Those who test positive in the UK are not usually given confirmatory tests as they are immediately required to isolate, resulting in a large number of current "cases" which may be false positives[3].

[1]https://www.anhinternational.org/news/is-there-a-waning-pand...

[2]https://www.thelancet.com/journals/lanres/article/PIIS2213-2...

[3]https://www.cebm.net/covid-19/pitfalls-of-repeat-testing-ill...

> vastly more preferable to a false negative

depending from the POV.

if a condition has an incidence of 0.001%, production capacity of test kits will probably be geared to that.

if you suddenly have 0.01% false positives, you're outstripping production by a factor of ten

it will also use up production capacity that might be necessary for other kits, driving up both test prices and/or wait time for everyone else.

for example: false positive in Italy are the reason you see a new case slowing down in the last week: https://www.google.com/search?client=firefox-b-d&q=italy+cov...

this is not because the containment measures are working, it's because a lot of tests are redirected to verify the PCR results, eating up test capacity and slowing down for example contact tracing tests, which are competing for the same kits.

so, no. false positives have far more implication than one individual short time of anxiety.

> false positives have far more implication than one individual short time of anxiety.

That was my point - for example in Liverpool 700 "asymptomatic cases" were found (0.4% of those tested) using lateral flow tests[1]. Well below the expected ~2.5% of the population currently expected to be infected, and well within a range which makes it likely that a significant proportion are false positives. All of these people will have been legally required to isolate for two weeks, many likely unable to work.

The problem with mass testing is that the false positive rate is far closer to the actual incidence.

[1]https://www.bbc.co.uk/news/uk-england-merseyside-54966607

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