The Small Area Predictors of Ambulatory Care Sensitive Hospitalizations: A Comparison of Changes over Time

Abstract

The hospital admission for ambulatory care sensitive conditions (ACSCs) is a validated indicator of impeded access to good primary and preventive care services. The authors examine the predictors of ACSC admissions in small geographic areas in two cross-sections spanning an 11-year time interval (1995–2005). Using hospital discharge data from the Healthcare Cost and Utilization Project of the Agency for Healthcare Research and Quality for Arizona, California, Massachusetts, Maryland, New Jersey, and New York for the years 1995 and 2005, the study includes a multivariate cross-sectional design, using compositional factors describing the hospitalized populations and the contextual factors, all aggregated at the primary care service area level. The study uses ordinary least squares regressions with and without state fixed effects, adjusting for heteroscedasticity. Data is pooled over 2 years to assess the statistically significant changes in associations over time. ACSC admission rates were inversely related to the availability of local primary care physicians, and managed care was associated with declines in ACSC admissions for the elderly. Minorities, aged elderly, and percent under federal poverty level were found to be associated with higher ACSC rates. The comparative analysis for 2 years highlights significant declines in the association with ACSC rates of several factors including percent minorities and rurality. The two policy-driven factors, primary care physician capacity and Medicare-managed care penetration, were not found significantly more effective over time. Using small area analysis, the study indicates that improvements in socioeconomic conditions and geographic access may have helped improve the quality of primary care received by the elderly over the last decade, particularly among some minority groups.

Keywords:

• Preventable hospitalizations
• small area analysis
• ambulatory care sensitive conditions
• quality of primary care
• changes over time

Notes

This research is funded wholly by the authors' employers, the Agency for Healthcare Research and Quality (AHRQ) and RTI International (Research Triangle Institute). The views expressed in this article are those of the authors. No official endorsement by any agency of the federal government is intended or should be inferred. The authors would like to acknowledge the state data organizations that participate in the HCUP State Inpatient Databases in Arizona, California, Oregon, Washington, Massachusetts, Maryland, New Jersey, and New York. The authors would also like to acknowledge the data and programming support provided by Social and Scientific Systems, Inc. in Maryland.

*Two-tailed t test indicates statistically significant differences between 1995 and 2005 (p < 0.05).

^aFor HRSA data and more explanations of the variables, see http://datawarehouse.hrsa.gov/.

^b1995 data are from Area Resource Files (ARF), county level, interpolated to represent PCSA.

1. In 2003, a pilot project was implemented which offered Preferred Provider Organizations (PPOs) with drug coverage to the elderly in 21 states, see Pope et al. (2005).

2. There are some gaps in the ZIP code tabulation area (ZCTA) coverage in very rural areas where no ZIP codes existed in 1990 or 2000, and there are no accompanying census data for these areas. These gaps correspond to the addresses for rural patients with no ZIP code (or giving a PO box that has no latitude or longitude). We did not encounter any problems, because all patients kept in the data set had residential ZIP codes.

3. The census data is nested by ZCTA inside the PCSAs, but the county data may span several PCSAs and cross their borders.