You can lead a horse to water--improving physicians' knowledge of probabilities may not affect their decisions

To determine whether improving physicians' judgments of the probability of streptococcal pharyngitis for patients with sore throats would affect their use of antibiotics and affect the variation in such use.

Post-hoc retrospective analysis of data previously collected as part of a controlled trial.

University student health services in Pennsylvania and Nebraska.

Sequential patients with pharyngitis seen before and after the time clinicians received either an experimental educational intervention designed to improve probabilistic diagnostic judgments (at the Pennsylvania site) or a control intervention, a standard lecture (at the Nebraska site). The clinician-subjects were the primary case physicians practicing at either site.

Clinical variables prospectively recorded by the clinicians, probability assessments, and treatment decisions.

At the experimental site, despite marked decreases in clinicians' overestimations of disease probability after the intervention, the proportion of patients prescribed antibiotics showed a trend toward increasing: 100/290 (34.5%) pre-intervention, 90/225 (40%) post-intervention. The intervention did not decrease practice variation between individual doctors. Univariable and multivariable analyses showed no major change in the relationships between clinical variables and treatment decisions after the intervention. At the control site there was no major change in probability judgments or treatment decisions after the intervention.

Teaching physicians to make better judgments of disease probability may not alter their treatment decisions.