Relation of Physicians' Predicted Probabilities of Pneumonia to Their Utilities for Ordering Chest X-rays to Detect Pneumonia

Abstract

To investigate the relation between physicians' predicted probabilities of pneumonia and their utilities for ordering chest x-rays to detect pneumonia, the authors studied 52 physicians who ordered chest x-rays of 886 patients presenting to an emergency department with fever or respiratory complaints Physicians estimated the probability of pneumonia prior to obtaining the results of the chest x-ray. Utilities were assessed by asking physicians to consider a hypothetical patient presenting with acute respiratory symptoms, with unknown chest x-ray status, and to rank on a scale from +50 ("best thing I could do") to - 50 ("worst thing I could do") their rating scale utilities for not diagnosing pneumonia and not ordering a chest x-ray when the patient had pneumonia (i.e, missing a pneumonia), and for diagnosing pneumonia and ordering a chest x-ray when the patient did not have pneumonia (i.e, ordering an unnecessary x-ray) The utility for ordering an unnecessary x-ray was negatively correlated with average predicted probability (r = -0 1495, p = 0 29), whereas the utility for missing a pneumonia was positively correlated with average predicted probability (r = 0 2254, p = 0.11), although the correlations were not statistically significant. Relative chagrin, defined as the difference in these utilities, was significantly inversely correlated with average predicted probability (r = -0 2992, p < 0.035), even after adjusting for the prevalence of pneumonia seen by each physician (partial r = - 0.42, p < 0 0027). It is concluded that physicians who experienced greater regret over missing a pneumonia than over ordering an unnecessary x-ray estimated lower probabilities of pneumonia for patients for whom they ordered x-rays. Thus, these physicians may have had lower thresholds for ordering chest x-rays for patients with acute respiratory illness. Key words: prediction, probability; utility, pneumonia. (Med Decis Making 1992;12:32-38)