Objective: To determine whether physicians’ post-test probability estimates are influenced by receiving test characteristics and impact their subsequent clinical decisions.
Design: Questionnaire based randomised controlled trial.
Setting: Mailed survey with a vignette describing an infant whose pretest likelihood of pertussis was 30% and direct fluorescent-antibody (DFA) test was negative for pertussis.
Subjects: Nationally representative sample of US paediatricians (n = 1502).
Interventions: Random receipt of no additional information (controls), the DFA’s sensitivity and specificity (TC group) or the test’s sensitivity and specificity with their definitions (TCD group).
Main outcome measures: Estimated post-test probability (PTP) of pertussis, PTP of 0.50, “nearly correct” PTP (±5%), intended erythromycin management and intended hospital disposition.
Analyses: χ2 and t tests.
Results: Despite the negative DFA result, 67% of the 635 (49.7%) participants who responded estimated a PTP higher than the pretest probability of 30%; the overall mean estimated PTP was 0.41 (SD 0.26) (correct answer: 0.18). The TCD group’s mean PTP was significantly higher than controls’ mean PTP (0.45 vs 0.38, p<0.001), while the TC and control groups’ mean PTP did not differ significantly (0.41 vs 0.38, p = 0.16). With decision support significantly more TC and TCD participants compared to controls estimated the PTP as 0.50 (38% vs 17%, p<0.001; 41% vs 17%, p<0.001, respectively) and also estimated a nearly correct PTP more often (20% vs 13%, p = 0.06; 19% vs 13%, p = 0.08, respectively). The mean PTP of participants intending to discontinue erythromycin therapy or discharge the patient home was significantly lower than that of participants who intended continuing erythromycin or hospitalisation (0.20 vs 0.43, p<0.001; 0.40 vs 0.49, p = 0.005, respectively).
Conclusions: Paediatricians differed in their response to information about test characteristics. For many, it increased errors in estimating post-test probability; for others, it reduced errors. Estimated post-test probability was logically associated with intended clinical management.
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