Methods:

Using Medicare administrative claims data from 2010, the investigators examined the relationship between regional density of cardiologists and risk of death after hospitalization for AMI and HF using hospitalizations for pneumonia as a comparison. They defined density as the number of cardiologists divided by population ages ≥65 years within hospital referral regions, categorized into quintiles. Among 171,126 admissions for AMI, 352,853 admissions for HF, and 343,053 admissions for pneumonia, the authors tested associations between density of cardiologists and 30-day and 1-year mortality for each condition. They used two-level hierarchical logistic regression models that adjusted for characteristics of patients and hospital referral regions.