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General Practice

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

BMJ 1999; 319 doi: (Published 10 July 1999) Cite this as: BMJ 1999;319:98
  1. Fiona D A Reid, lecturer in medical statistics (freid{at},
  2. Derek G Cook, professor of epidemiologya,
  3. Azeem Majeed, senior lecturer in general practiceb
  1. a Department of Public Health Sciences, St George's Hospital Medical School, London SW17 0RE
  2. b Department of General Practice and Primary Care, St George's Hospital Medical School
  1. Correspondence to: F D A Reid
  • Accepted 28 April 1999


Objectives: To 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.

Design: Cross sectional analysis of routine data.

Setting: Merton, 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 measures: Hospital admission rates for general practices for overall, emergency, and elective admissions.

Results: Crude 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.

Conclusions: Hospital 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.

Key messages

  • There is substantial variation in hospital admission rates between general practices

  • Patient factors were by far the most important in explaining this variation whereas general practice characteristics explained a negligible amount, providing little help to those with an interest in managing admissions

  • Deprivation was more strongly related to emergency rather than to elective admission rates, raising issues around equity of healthcare provision

  • Admission rates should be standardised for differences in patient populations and hospitals used to give fair and meaningful comparisons between general practices

  • Improvements in the quality of routine health services data are essential to enable health authorities and primary care groups to interpret information correctly


  • Funding FDAR is partly funded by Merton, Sutton, and Wandsworth Health Authority

  • Competing interests None declared.

  • Accepted 28 April 1999
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