Was the test (or cluster of tests) validated in a second, independent group of patients?
The tests should be assessed in an independent 'test' set of patients. This question is important in studies looking at multiple diagnostic elements.
If the study fails any of the above criteria, we need to consider if the flaw is significant and threatens the validity of the study. If this is the case, we'll need to look for another study. Returning to our clinical scenario, the paper we found satisfies all of the above criteria and we will proceed to assessing it for importance.
- Was there an independent, blind comparison with a reference ("gold") standard of diagnosis?
- Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom we would use it in practice)?
- Was the reference standard applied regardless of the diagnostic test result?
- Was the test (or cluster of tests) validated in a second, independent group of patients?