During validation of a diagnostic test a false positive event is observed in 1 out of 60 occasions leading to a specificity of 98.3% when testing for a single event. If 30 events are looked for using this test at a single time point and detection of a single event is considered a positive result, then would we expect the specificity of this test to be 50%, since there is a 30 x 1/60 probability of detecting a false positive event?If we increase the threshold for what we consider a positive result to the detection of 2 events then would we expect the specificity to be 99.2% i.e. a 30 x (1/60 x 1/60) probability of detecting two false positive events

I wonder if this may be more complicated than above and whether specificity can be predicted in this fashion.

Many thanks!

I wonder if this may be more complicated than above and whether specificity can be predicted in this fashion.

Many thanks!

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