There's a difference between false positive rate and positive predictive value: https://en.wikipedia.org/wiki/False_positive_rate https://en.wikipedia.org/wiki

There's a difference between false positive rate and positive predictive value: https://en.wikipedia.org/wiki/False_positive_rate https://en.wikipedia.org/wiki/False_positive_rate https://en.wikipedia.org/wiki/Positive_and_negative_predictive_values https://en.wikipedia.org/wiki/Positive_and_negative_predicti... The latter depends on the prevalence of the test condition in the population, which is one of the major points of the OP. A test can have a low false positive rate but still have a low positive predictive value if the test condition is sufficiently rare (as it is for most diseases). brianwawok was probably referring to tests with a low positive predictive value.