Theory 91/Selection & Bias/Screening
Screening Detects on a Schedule
The claim
Screening programmes detect preferentially the cases that pass through the test window at the right time, so incidence in screened groups is artificially raised.
01Mechanism
A case is detected only if it is present at screening; cases that would have appeared between tests are counted later or not at all.
02Prediction
Screened cohorts should show higher apparent incidence.
03Refutation
Equal incidence across screened and unscreened would remove the bias.