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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▸ Additional information is published online only at http://adc.bmj.com/content/vol94/issue3
Funding: This work was conducted while CMS was a Robert Wood Johnson Clinical Scholar at the University of Washington. The Robert Wood Johnson Generalist Physician Faculty Scholar program supported DAC. The opinions are those of the authors and not the Robert Wood Johnson Foundation (Princeton, New Jersey, USA). This study was supported in part by the Nesholm Family Foundation (Seattle, Washington, USA). The authors’ work was independent of the funding organisations.
Competing interests: None.
Ethics approval: The University of Washington Institutional Review Board approved this study.
Some of the results of this study were presented at the 2004 annual meetings of the Society for Medical Decision Making and the Pediatric Academic Society, as well as the 2003 Robert Wood Johnson Clinical Scholars Program national meeting.
Contributions: All authors participated in the study design and interpretation of the data, and contributed to revision of the manuscript. CMS and DAC came up with the idea for the study. CMS collected and analysed the data, wrote the first draft and finalised the manuscript, and is guarantor.
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