Methods: Two cross-national video vignette factorial experiments were conducted in the US and UK to estimate 256 generalist physicians' diagnostic and treatment decisions for actor “patients” depicting CHD or depression. Patient factors were gender, age (55 or 75 years), race (white or black), and socioeconomic status (SES) (cleaner/janitor or school teacher). Physician factors were gender and level of experience.

Results: For both conditions, US physicians were more certain than their UK counterparts. For CHD, physicians were more certain with male patients and least certain with younger female patients. Physicians in the US were more certain than UK physicians if the patient was white. If the patient was black, US and UK patients were equally certain. Less experienced physicians were less certain with black patients and female physicians were less certain for lower SES patients. For depression, patient factors alone were not significant predictors of certainty. However, male physicians had higher certainty with younger patients and female physicians were more certain with older patients. In turn, certainty affected several CDM behaviors. For CHD, certainty is positively correlated with the number of questions asked, number of tests ordered and with prescribing CHD-specific medications. Physicians more certain of the CHD diagnosis are more likely to prescribe CHD-specific medications (Odds ratio (OR) 1.62, 95% confidence interval (CI) 1.43-1.84, per 10 point increase in certainty on a 100 point scale). For depression, certainty is not associated with questions or test ordering. Physicians more certain of the depression diagnosis are more likely to prescribe antidepressants (OR 1.98, 95% CI 1.50-2.61, per 10 point increase in certainty).

Conclusions: In a factorial video vignette experiment, we observe significant variation in physician certainty and CDM among physicians in two countries (US and UK) and for two conditions (CHD and depression). In various combinations, patient characteristics, provider attributes, country, and interactions among those factors are all significant predictors of certainty and CDM. Together, these findings suggest that some healthcare variations in clinical decisions making (test-ordering, prescribing, etc.) may be caused by physician uncertainty.