Family Practice Vol. 21, No. 4, 355-363
Family Practice Vol. 21, No. 4 © Oxford University Press 2004, all rights reserved.
Adjusting for case mix and social class in examining variation in home visits between practices
a Public Health Policy Unit, School of Public Policy, University College London, London WC1H 9QU, b Medical Statistics Unit, Research and Development Directorate, University College London Hospitals NHS Trust, London WIP 9LL, c Department of Statistical Science, 1–19 Torrington Place, University College, London WC1E 6BT, UK and d Health Services Research and Development Center, Department of Health Policy and Management, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 21205, USA
Correspondence to Caoimhe O Sullivan, Medical Statistics Unit, Research and Development Directorate, University College London Hospitals NHS Trust, Maple House, 149 Tottenham Court Road, London WIP 9LL, UK; E-mail: caoimhe.osullivan{at}uclh.nhs.uk
Objectives. The purpose of this study was to investigate whether adjusting for clinical case mix and social class explains more of the variation in home visits between general practices than adjusting for age and sex alone.
Methods. The setting was 60 general practices in England and Wales taking part in the 1 year Fourth National Morbidity Survey. The participants comprised 349 505 patients who were registered with one of the participating general practices for at least 180 days, and who had at least one consultation during the period. The outcome measure is whether or not a patient received a home visit in that year. A clinical case mix category (morbidity class) based on 1 year's diagnostic information was assigned to each patient using the Johns Hopkins Adjusted Clinical Groups (ACG) Case Mix System. The social class measure was derived from occupation and employment status and is similar to that of the 1991 UK census. Variations in home visits between practices were examined using multilevel logistic regression models. The variability between practices before and after adjusting for clinical case mix and social class was estimated using the intracluster correlation coefficient (ICC).
Results. The overall percentage of patients receiving a home visit over the 1 year study period was 17%, and this varied from 7 to 31% across the 60 practices. The percentage of the total variation in home visits attributable to differences between practices was 2.5% [95% confidence interval (CI) 1.4–3.2%] after adjusting for age and sex. This reduced to 1.6% (95% CI 1.1–2.4%) after taking into account morbidity class. The results were similar when social class was included instead of morbidity class. Morbidity and social class together reduced variation in home visits between practices to 1.5% (95% CI 1.1–2.2%).
Conclusions. Age, sex, social class and clinical case mix are strong determinants of home visits in the UK. Adjusting for morbidity and social class results in a small improvement in explaining the variability in home visits between practices compared with adjusting for age and sex alone. There is far more variation between patients within practices; however, it is not straightforward to examine the factors influencing this variation. In addition to morbidity and social class, there could also be other unmeasured factors such as varying patient demand for home visits, disability or differences in GP home visiting practice style that could influence the large within-practice variability observed in this study.
Keywords. Case mix, home visits, practice variation, primary care.
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