Health Service Areas (HSAs) are a compromise between the 3000 counties and the 50 states. An HSA may be thought of as an area that is relatively self-contained with respect to hospital care and may cross over state boundries. HSAs have been defined in a number of ways in the literature. We use the HSAs determined by Makuc et al. (1991) and extended by Pickle et al. (1996). These HSAs were formed using a clustering algorithm applied to 1988 Medicare data on short-stay hospital visits. There are approximately 800 HSAs in the United States.References
Makuc DM, Haglund B, Ingram DD, Kleinman JC, Feldman JJ. Health service areas for the United States. Vital Health Stat 2 1991 Nov;(112):1-102.
Pickle LW, Mungiole M, Jones GK, White AA. Atlas of United States mortality. Hyattsville, Maryland: National Center for Health Statistics, 1996.