Explaining variation in hospital admission rates between general practices: cross sectional study.

objectivesTo quantify the extent of the variation in hospital admission rates between general practices, and to investigate whether this variation can be explained by factors relating to the patient, the hospital, and the general practice.

designCross sectional analysis of routine data.

settingMerton, Sutton, and Wandsworth Health Authority, which includes areas of inner and outer London. SUBJECTS: 209 136 hospital admissions in 1995-6 in patients registered with 120 general practices in the study area.

main outcome measuresHospital admission rates for general practices for overall, emergency, and elective admissions.

resultsCrude admission rates for general practices displayed a twofold difference between the 10th and the 90th centile for all, emergency, and elective admissions. This difference was only minimally reduced by standardising for age and sex. Sociodemographic patient factors derived from census data accounted for 42% of the variation in overall admission rates; 45% in emergency admission rates; and 25% in elective admission rates. There was a strong positive correlation between factors related to deprivation and emergency, but not elective, admission rates, raising questions about equity of provision of health care. The percentage of each practice's admissions to different local hospitals added significantly to the explanation of variation, while the general practice characteristics considered added very little.

conclusionsHospital admission rates varied greatly between general practices; this was largely explained by differences in patient populations. The lack of significant factors related to general practice is of little help for the direct management of admission rates, although the effect of sociological rather than organisational practice variables should be explored further. Admission rates should routinely be standardised for differences in patient populations and hospitals used.