Does Market Structure Affect Access to Ambulatory Care?: The Relationship Between Provider Supply, Inter-organizational Relationships, and Ambulatory Care Sensitive Hospitalizations.

Abstract

Adequate access to health services remains a fundamental challenge for the U.S. health care system. Ambulatory care sensitive hospitalizations (ACSH) are increasingly used as indicators of access in health services research. Importantly, most empirical research on ACSH has overlooked or narrowly defined the role of organizations in improving or impeding access. Using a coordination-and-control theoretical framework, this study examined whether the structural characteristics of markets such as provider capacity, provider composition, and inter-organizational relationships affect acute care, chronic care, and aggregate ACSH rates. The study used a longitudinal, pooled cross-sectional design that examined 58 California markets for the years 1998 through 2005. The unit of analysis was the market-year and the final analytic sample included 450 observations.

The most robust findings pertained to provider composition, where the ratio of home health agencies, skilled nursing facilities, and physician organizations to hospitals were significantly and negatively associated with ACSH rates. Provider capacity and inter-organizational relationships generally failed to demonstrate significant relationships with ACSH rates. Contrasting results between provider capacity and provider composition suggest that the effects of provider supply may depend upon how supply is measured.

Supplementary analysis examined these relationships on a condition-specific basis and suggested that the effects of inter-organizational relationships may be limited to specific clinical conditions. Specifically, the analysis found that the proportion of hospitals with a formal physician organization relationship was associated with higher hospitalization rates for pneumonia, angina, asthma, and congestive heart failure. In contrast, the proportion of hospitals in a market with a formal nursing home relationship was significantly associated with lower hospitalization rates for perforated appendix, angina, asthma, and hypertension. Likewise, the proportion of hospitals in a market that owned an insurance product was associated with lower hospitalization rates for congestive heart failure, chronic obstructive pulmonary disease, and uncontrolled diabetes. These results suggest that the relationship between market structure and ACSH rates may depend upon the medical condition and the type(s) of organizations under study. Overall, these findings raise questions about the appropriateness of combining clinical conditions into aggregated hospitalization rates and the conclusions of studies that use such approaches to study ACSH.