Small-area variations in rates of hospitalization and surgery within Rhode Island.

We analyzed variations in the usage rates and costs of 13 surgical procedures among 37 cities and towns in the state of Rhode Island. To compare different operations and years, we defined the deviation index, a percentage indicator similar to the coefficient of variation, but with chance variation removed. Tonsillectomy and disc excision were the procedures for which rates varied most around the state average; their deviation indexes for 1981 were 40.5 percent and 38.9 percent, respectively. In 14 areas, rates for one of these two procedures (standardized for age and sex) were significantly (p less than .01) above or below the state average; such outlying observations would have been expected for only one area if rates had been uniform statewide. To indicate the relative amount of surgery in an area combining rates for all 13 procedures, we computed the area's surgical index. This index, the average of the ratios of observed to expected cases (based on standardized statewide rates), doubled from the lowest- to the highest-rate areas. Overall, surgical hospital days, nonsurgical days, total hospital days, and hospital costs (all per 1,000 population) doubled from lowest- to highest-rate areas. If the rates of these 13 surgical procedures could be lowered in high-rate areas to not more than 20 percent above the state average, usage could drop by 4 percent. We conclude that even within the small state of Rhode Island, surgical practice varies considerably across communities. Identifying and studying areas with extremely high or low rates should enable more explicit consideration of the indications for surgery and perhaps lead to lower costs for medical care.