Geographical variation in hospital admission rates: an analysis of workload in the Oxford region, England.

OBJECTIVE:To measure variation in hospital admission rates between health districts in part of the English NHS, comparing a wide range of medical and surgical conditions. DESIGN:Retrospective analysis of interdistrict variation using linked routine hospital admission data. Comparisons were also made with levels of variation reported from the USA. SETTING:Oxford Regional Health Authority, 1979-86. SUBJECTS:Six district health authorities--total study population 2.1 million people, 1.6 million hospital admissions. MAIN MEASURES:Age and sex standardised hospital admission rates for resident populations for individual operations and diagnoses; systematic components of variation (SCV). RESULTS:Of 118 standard operation groups, 38 (26% of surgical workload) showed high variation (SCV 16 or more) and 40 (36% of surgical workload) showed low variation (SCV < 4). Operations (SCV) with very low levels of variation included prostatectomy (0.1), inguinal herniorraphy (0.9), and cholecystectomy (1.3). Rates were more variable for myringotomy (3.7), hysterectomy (4.3), dilatation and curettage (5.6), and tonsillectomy (6.2). The SCV was high for only four of the 40 commonest medical causes of admission, and was low for 18 of them. CONCLUSIONS:Most admissions in the Oxford region were for conditions that did not show a great deal of variation in admission rates. The level of variation for many surgical procedures was less than that reported in studies from the USA. Variation was no greater for medical causes of admission than for surgical conditions. Large scale variation may not be an inevitable consequence of autonomous clinical practice.