Does Region Hold the Key to the Paradox?
One potentially important limitation of the earlier analysis is that it assumes that the effect of physician supply on mortality is constant for all counties across the country. There are many reasons this relationship might not hold. County size varies widely—the average county in Arizona is 36 times larger (in land area) than the average county in Rhode Island. The extent to which the county is a useful approximation of the market for primary care services may vary widely. Secondly, the relationship between primary care and mortality may vary regionally due to local practice patterns. Evidence suggests that physician practice patterns vary across the country (Goodman et al. 1996; Fisher and Wennberg 2003) and that there is significant variation in the supply of practitioners (Goodman et al. 2003) as well as the outcomes of care (Wennberg, Fisher, and Skinner 2004). The extent to which these practice patterns affect mortality will condition the effect of supply on mortality. Finally,
