> On the other hand PCR test are not inaccurate at all, at least regarding false positives.
PCR tests work by selectively amplifying DNA. Each PCR test cycle approximately doubles the amount of the selected DNA. (for SARS-CoV-2, an RNA virus, the RNA is first converted to DNA)
Since each cycle approximately doubles the amount of selected DNA present, PCR tests can be extraordinarily sensitive if enough cycles are used. In theory, just a single fragment of RNA could result in a positive test. As Health Canada says:
"There are numerous studies that demonstrate prolonged detection of SARS-CoV-2 RNA that extends beyond the resolution of COVID-19 symptoms and can persist for several weeks or months." https://www.canada.ca/en/public-health/services/diseases/201...
Hospitals are testing pretty much everyone who comes in the door for COVID-19. The fact that people can test positive long after they were actually infected should obviously raise questions about the accuracy of our statistics with regard to COVID-19 hospitalization and death rates.
Additionally, contamination is a potential problem. For example, the BBC's undercover reporting found significant cross-contamination between samples at one testing lab: https://www.bbc.com/news/uk-56556806
Contamination could be showing up as a multiplier on true positives: as positive % increases, opportunities for contamination also increase. Since PCR tests work by replicating DNA, they also have the unusual property that the testing process itself creates large quantities of potential contamination. Good lab practice will eliminate that problem. But that's hard to guarantee when testing volume is increased enormously in a short period of time.