Mortality and physician supply: does region hold the key to the paradox?

Recently there has been a series of research reports that have described positive associations between the supply of primary care physicians and health outcomes (Shi 1992, Shi, 1994; Forrest and Starfield 1996; Shi et al. 2003a, Shi et al. 2003b, Shi, 2005; Starfield et al. 2005; Starfield, Shi, and Macinko 2005). This favorable association of medical resources and health has not always been accepted. The contribution of medical resources to population health status has long sparked vigorous debate. Medical care, it has been argued, contributed little to the dramatic reduction in overall mortality rates in the twentieth century (McKeown 1979). Analysis of long-term mortality trends in the United States from 1900 to 1973 found that medical care could account for very little of the overall decline in mortality (McKinlay and McKinlay 1977). Other studies found that the supply of physicians has been observed to have a “persistent but puzzling positive correlation” with mortality rates that could not be “adjusted away” by covariates such as income (Young 2001). An explanation was offered by Young (2001) that growing industrial cities “attract an oversupply of doctors and also attract rural immigrants whose health breaks down in the context of city life.” Other investigators have replied that this may be an artifact and that associating long-term mortality trends to physician supply did not reflect a lack of contribution by the medical profession, and that “such evidence is not to be interpreted to mean that medical care is not important, but rather it suggests that other factors have contributed to the decline in mortality” (Kindig 1997). Negative relationships (more physicians associated with lower mortality) have been reported for the United States for overall physician supply (Kindig, Seplaki, and Libby 2002) as well as for the supply of primary care physicians (Starfield et al. 2005). These analyses, with the exception of the work reported by Kindig, Seplaki, and Libby (2002), have generally accepted the applicability of the geographical units of analysis that are used to aggregate the indicator of medical resources and which provide the denominator for the mortality rate. These have included U.S. counties, cities and metropolitan areas, or nations. They have not considered regional effects or variations in the size of the denominator areas. This paper explores whether those geographical aspects of the units of analysis may contribute to the patterns of correlation of practitioner supply and mortality. This study builds on a previously published work by Starfield et al. (2005), examining the relationship between mortality and primary and specialty physician supply, and attempts to replicate those results while controlling for the effects of geography. Examining pooled mortality data for U.S. counties from 1996 to 2000, that study found that U.S. counties with higher supply of primary care physicians have lower mortality; while counties with a higher supply of specialists generally have higher mortality. The earlier study suggested that any policies intended to improve health outcomes for underserved areas ought to concentrate on strengthening primary care resources and that this could be achieved at the local level. One goal of this analysis is to determine if the effect is consistent across all regions of the United States and, when regional patterns are considered, whether that effect remains. We extend the analysis by accounting for possible specification problems, both statistical and geographical, that might lead to different conclusions and hence to different policies. If the earlier analysis holds, policy emphasis should be placed upon the strengthening of local primary care supply to meet effective minimum if not optimal levels. If there are regional effects, alternative policies may be better, including the support of regional systems and using both specialist and primary care supply standards for determining whether a community qualifies for governmental support.