Proficiency bias occurs when interventions are not applied equally to different study participants because of differences in skill, training, resources, or procedures used at different sites or by different practitioners in the study.
Point of care ultrasound is an area of medicine with a wide variance in proficiency. A study comparing the FAST scan in pediatric and adult emergency departments might conclude that the FAST scan is less accurate in pediatrics, but those results could be biased if pediatric clinicians are generally less skilled or experienced in ultrasound.
Proficiency could also impact the generalizability of results from a study. In the hands of experts, ultrasound has been shown to be very accurate in many emergency scenarios, but it isn’t clear that I should apply to my practice, as I am certainly less skilled the the participants in those trials.
Proficiency bias is a type of intervention bias.