Improving Your Critical Appraisal Skills #5

Part 2 of Diagnostic Tests

The previous post in this series covered test characteristics and other metrics (positive and negative predictive value) of diagnostic tests. It also dove a bit into clinical reasoning. This post covers receiver operator characteristic curves and common problems in diagnostic test articles: spectrum bias, work up bias, and issues with reproducibility.

But first... a little test characteristic practice.

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Question #1

Two studies define the test characteristics for rheumatoid factor (RF) in the diagnosis of rheumatoid arthritis (RA). Both run with the same assay in people with RA and age and sex matched controls. The gold standard in both studies is the diagnosis of RA by a team of expert rheumatologists. The results for the studies were as follows:

Study #1: sensitivity, 80%; Specificity, 95%.

Study #2: sensitivity, 82%; Specificity, 15%

Question: How can they have such different results?