The effects of communicating illness diagnostic and treatment information and C‐reactive protein test results on people's antibiotic expectations

<jats:title>Abstract</jats:title><jats:sec><jats:title>Objectives</jats:title><jats:p>Patients' expectations for antibiotics are among the strongest predictors of clinicians' decisions to overprescribe antibiotics. In this registered report, we used a signal detection theory framework to investigate the experimental effects of the communication interventions that family physicians can use to reduce patients' diagnostic uncertainty, and consequently, their antibiotic expectations.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>UK participants (<jats:italic>N</jats:italic> = 769) read hypothetical consultations for respiratory tract infections and were randomly assigned to one of three conditions: standard information (control), recommended information about the nature of the illness and antibiotic efficacy (recommended communication) or recommended information accompanied by point‐of‐care test results (recommended communication and CRP). Using a multilevel Bayesian probit regression, we estimated both decision bias (criterion) and sensitivity (d‐prime).</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Aligned with our bias hypotheses, participants displayed a more liberal antibiotic bias in the control condition compared to both the recommended communication (Δ<jats:italic>c</jats:italic> = −1.34, 95% CI [−1.57, −1.11]) and the recommended communication and CRP (Δ<jats:italic>c</jats:italic> = −1.73, 95% CI [−1.99, −1.48]) conditions. They also showed greater liberal bias in the recommended communication condition compared to the recommended communication and CRP condition (Δ<jats:italic>c</jats:italic> = −0.39, 95% CI [−0.65, 0.13]). Aligned with our sensitivity hypotheses, participants displayed significantly higher sensitivity in both the recommended communication (Δ<jats:italic>d</jats:italic>' = 2.34, 95% CI [1.92, 2.79]) and the recommended communication and CRP (Δ<jats:italic>d</jats:italic>' = 2.49, 95% CI [2.08, 2.95]) conditions compared to control.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>Simple, evidence‐based communication strategies—particularly when combined with diagnostic test results—can reduce antibiotic expectations, offering practical tools for clinicians to support appropriate prescribing.</jats:p></jats:sec>