Variation in hospital admissions among small areas. A comparison of Maine and Michigan.

Analysis of age-adjusted hospital admission profiles among small geographic areas has shown marked variation in hospital admissions for both surgical and medical cases in areas ranging from Maine to Manitoba. Much of the work has been led by John Wennberg and has focused on rural areas. This study examines the degree of variation in hospital admissions in small areas in the state of Michigan to determine whether those diseases that demonstrated high variation in Maine also demonstrated the same degree of variation in Michigan. The data on the degree of variation in 111 modified diagnosis-related groups (M-DRGs) from the state of Maine were supplied by Dr. Wennberg. Using the same M-DRGs, we defined age-adjusted, population-based hospital admission rates for the lower peninsula of Michigan for 1980 among 60 previously defined hospital marked communities. The observed hospital discharge counts in each of the M-DRGs were compared to the expected counts in each of the 60 communities, where the expected count was based on an indirect age adjustment. Both the Maine and Michigan small area data were expressed by the M-DRG's systematic standard deviation in which random variation has been accounted for via a Poisson probability model. It was found that the systematic standard deviations of the M-DRGs in Maine and the M-DRGs in Michigan strongly correlated with a Spearman correlation coefficient of 0.71 (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)