Can prevalence expectations drive radiologists' behavior?

RATIONALE AND OBJECTIVES: To measure the effect of explicit prevalence expectation on the performance of experienced radiologists during image interpretation of pulmonary lesions on chest radiographs. MATERIALS AND METHODS: Each of 22 experienced radiologists was allocated to one of three groups to interpret a set of 30 (15 abnormal) posteroanterior chest images on two occasions to decide if pulmonary lesions were present. Before each viewing, the radiologists were told that the images contained a specific number of abnormal images: group 1, 9 versus 15; group 2, 22 versus 15; and group 3, not told versus 15, respectively. Eye position metrics and receiver operating characteristics confidence ratings were compared for normal and abnormal images. An analysis of false-positive and false-negative decisions was also performed. RESULTS: For normal images, at higher prevalence expectation, significant increases were noted for duration of image scrutiny (group 1: P = .0004; group 2: P = .007; and group 3: P = .003) and number of fixations per image (group 1: P = .0006; group 2: P = .0004; and group 3: P = .0001). Also for normal images, group 1 demonstrated a significant increase (P = .038) in average confidence ratings when prevalence expectation increased. For abnormal images, at higher prevalence expectation, significant increases were noted for duration of image scrutiny in group 1 (P = .005) and number of fixations per image in group 1 (P = .01) and group 2 (P = .003). CONCLUSIONS: Confidence ratings and visual search of the expert radiologists appear to be affected by changing prevalence expectations. The impact of prevalence expectation appears to be more apparent for normal images.