Healthy User Bias in Comparative Safety Studies for Brand‐Name vs. Generic Products: The Example of Warfarin

Warfarin was selected as a case study to examine confounding when comparing a product across different manufacturers because it is a narrow therapeutic index drug with prevalent beliefs for brand‐name superiority. Medicare beneficiaries aged ≥65 years with atrial fibrillation and an incident outpatient warfarin prescription from July 2006 through July 2015 were included in the study population ( N = 746,098). Substantial imbalances were observed...