[koolba]

Is there “error” for these these tests independent when performed on the same person spaced out over a long enough time period?

Say you run the test every day/week/month, can you look at the total results or do the failure cases for the tests themselves depend on the individual?

[nugget]

Many diagnostic blood tests for cancer markers are more useful as a data series over time than as single point in time tests, because individuals have variable "normal" or baseline levels. You establish an individual baseline for each marker (for each patient) and then re-test every 6 months. If a number moves from its baseline, then you investigate.