Effect of case mix on provider continuity.

A random sample of 265 patient charts was selected to assess the degree of provider continuity at the University of North Carolina Family Practice Center from July 1, 1983, to June 30, 1984. Continuity was measured using usual provider continuity, the ratio of the number of visits with the assigned physician divided by total visits. Usual provider continuity rates varied as predicted for three types of visits: acute illness (0.55), chronic illness (0.76), and health maintenance (0.86). The average rate of usual provider continuity was 0.68. Case mix had a statistically significantly effect on provider continuity when comparing acute care with either chronic or health maintenance care (P less than .01). Because case mix is relevant and varies from site to site, a method of rate standardization was suggested using data on case mix from the National Ambulatory Medical Care Survey. Direct rate adjustment, a standard epidemiologic technique, would make continuity rates directly comparable for sites with different case mixes.