Understanding sources of bias in diagnostic accuracy studies.

CONTEXT Accuracy is an important feature of any diagnostic test. There has been an increasing awareness of deficiencies in study design that can create bias in estimates of test accuracy. Many pathologists are unaware of these sources of bias. OBJECTIVE To explain the causes and increase awareness of several common types of bias that result from deficiencies in the design of diagnostic accuracy studies. DATA SOURCES We cite examples from the literature and provide calculations to illustrate the impact of study design features on estimates of diagnostic accuracy. In a companion article by Schmidt et al in this issue, we use these principles to evaluate diagnostic studies associated with a specific diagnostic test for risk of bias and reporting quality. CONCLUSIONS There are several sources of bias that are unique to diagnostic accuracy studies. Because pathologists are both consumers and producers of such studies, it is important that they be aware of the risk of bias.