The Impact of Health Insurance Expansion on Physician Treatment Choice: Medicare Part D and Physician Prescribing

We test the effect of the introduction of Medicare Part D on physician prescribing behavior by using data on physician visits from the National Ambulatory Medical Care Survey (NAMCS) 2002-2004 and 2006-2009 for patients aged 60-69. We use a combined DD-RD specification that is an improvement over either the difference-in-difference (DD) or regression discontinuity (RD) designs. Comparing the discrete jump in outcomes at age 65 before and after 2006, we find a 35% increase in the number of prescription drugs prescribed or continued per visit and a 55% increase in the number of generic drugs prescribed or continued, providing evidence of physician response to changes in patient out-of-pocket costs.