Does Physician Specialty Affect the Survival of Elderly Patients with

Objective. To determine the effect of treatment by a cardiologist on mortality of elderly patients with acute myocardial infarction (AMI, heart attack), accounting for both measured confounding using risk-adjustment techniques and residual unmea-sured confounding with instrumental variables (IV) methods. Data Sources/Study Setting. Medical chart data and longitudinal administrative hospital records and death records were obtained for 161,558 patients aged> 65 admitted to a nonfederal acute care hospital with AMI from April 1994 toJuly 1995. Our principal measure of significant cardiologist treatment was whether a patient was admitted by a cardiologist. We use supplemental data to explore whether our anal-ysis would differ substantially using alternative definitions of significant cardiologist treatment. Study Design. This retrospective cohort study compared results using least squares (LS) multivariate regression with results from IV methods that accounted for addi-tional unmeasured patient characteristics. Primary outcomes were 30-day and one-year mortality, and secondary outcomes included treatment with medications an