Studies of diagnostic test accuracy: Partial verification bias and test result-based sampling.

BACKGROUND

Partial verification bias occurs in studies assessing the accuracy of existing diagnostic tests when a positive index test makes application of the reference standard more likely.

METHODS

This article first describes alternative sampling frames for a diagnostic test accuracy study then discusses partial verification bias.

RESULTS

One approach to avoiding partial verification bias is to apply the reference standard to all individuals who are positive on the index test and a random sample of those who are negative. Estimating sensitivity and specificity then requires adjusting for the sampling fraction in the test-negative group.

CONCLUSION

If a finding was already used to determine who should get the definitive test, one can't look at those who got the definitive test to determine the usefulness of the finding.