I came across this article from the NY Times last year – my first awareness of the problems of the fabled PCR test.
Later, a few weeks I recall, Professor Carl Heneghan said up to 50% may be false positives. I taught myself the basics of calculating the false positives rates (and false negatives too) and agrred with the professor. You’ll need to know the prevalence rate of the disease at any one period in time.
The lower the prevalence rate the more false positives.
Note: They have another trick up their sleeves … the amplification rate.