Preventable Hospitalization Patterns of Medicare Beneficiaries and Propensity to Travel Outside Local Markets

We investigate the determinants of preventable hospitalization patterns of Medicare beneficiaries who travel outside their local markets. Local markets have been defined for the Health Resources and Services Administration (HRSA) as primary care service areas (PCSAs), which were built from analysis of patient flows to primary care physician offices. Since preventable hospitalizations are indicators of poor access to primary care services, PCSAs are a relevant market unit for this spatial analysis of patient travel patterns. Most previous studies of preventable hospitalizations have used measures based on the county of patient residence, which is much larger than the PCSA and certainly too large to describe local markets in the western United States, where counties are large. For example, California has 58 counties and 335 PCSAs. We examined HCUP-SID data for Medicare beneficiaries hospitalized within the state of California (CA) for preventable conditions both in 2001 and 2004. The patient-level information obtained from discharge data for CA hospitals was linked to PCSA-level contextual variables. These variables were constructed from the Medicare enrollment data base and the US census of populations, and many of them are available to researchers via HRSA's online spatial data warehouse. We employ logistic regression to study determinants of the likelihood that a Medicare beneficiary would be hospitalized outside his/her PCSA for preventable conditions. Of particular interest is the association between patient hospitalization patterns and characteristics of the local areas, holding patient demographics and illness severity constant. The study examines a range of local area characteristics including physician availability, inpatient capacity, outpatient utilization patterns, socioeconomic characteristics such as income and language ability, managed care penetration levels, the availability of critical access hospitals, and the prevalence of international medical graduates relative to native US doctors. In the analysis of California healthcare markets, we found that Medicare beneficiaries were more likely to bypass their local market hospitals if they lived in areas with very high or very low income, higher Medicare HMO penetration, or in more rural areas. Patients who were nonwhites, HMO enrollees, males, younger elderly, or more severely ill were more likely to go out of the area. We also found that the supply of local resources, such as primary care physicians, higher prevalence of foreign medical graduates, and availability of critical access hospitals contribute to the retention of patients within their PCSAs. The analysis of 2004 data reveal additional characteristics of the areas. For example, areas with higher proportions of foreign language speaking households that are linguistically isolated were likely to have higher patient retention rates. For patients residing in rural areas, higher inpatient capacity provided by local hospitals was found to reduce the likelihood of hospitalization outside the area. These findings suggest that federal subsidies to rural or critical access hospitals may have helped ease shortages of medical services in their communities. Using a different approach to define local areas as PCSAs, rather than counties, our findings support previous policy conclusions that developing local resources is beneficial for the retention of the elderly close to home. In ongoing work, we plan to include other states in the United States in further analysis for this paper.