• C A Woodward and J Hurley.
• Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ont.
• CMAJ. 1995 Oct 15;153(8):1097-106.

ObjectiveTo examine the extent to which physician's sex explains variation in the activity level and service intensity of a cohort of physicians in each of five medical fields after other sources of variation are taken into account.DesignData from the Ontario Ministry of Health (MOH) and the CMA were analysed by means of multivariate regression techniques for panel data.SettingOntario.ParticipantsA total of 137 dermatologists, 974 general internists, 330 pediatricians and 941 psychiatrists and a random sample of 2771 family physicians and general practitioners who met the eligibility criteria. Physicians were eligible if they billed the MOH for at least three quarters in 1983, did not bill as a medical laboratory director, provided direct patient care, did not have an alternative funding arrangement with the MOH, remained in the same specialty throughout the study period (1983-90) and billed from an Ontario address.Outcome MeasuresThree measures of total activity level (annual number of services provided, annual fee-for-service billings and annual mean number of patients seen per quarter) and one measure of service intensity (annual mean number of services per patient per quarter).ResultsAlthough several variables (e.g., full-time work status, age, type of practice and recent practice move) influenced the four measures examined, physician's sex contributed significantly to explaining variation in activity in 70% of the regression equations. The women provided 33.0% fewere services per year than the men in family and general practice (p < 0.001), 25.0% fewer services in general internal medicine (p < 0.01), 22.1% fewer services in pediatrics (p < 0.05) and 22.3% fewer services in psychiatry (p < 0.001). Total billings by the women in these fields were also significantly less than those of their male colleagues, the difference being greatest among the family physicians and general practitioners (28.0%) and the general internists (27.0%) (p < 0.001). The women in these four fields saw significantly fewer patients per quarter than their male colleagues, the difference being greatest in psychiatry (33.0%) (p < 0.001). Sex affected service intensity in three fields. The female psychiatrists (14.8%) (p < 0.001) and general intenists (5.5%) (p < 0.10) provided more services per quarter than their male colleagues, whereas the female family physicians and general practitioners delivered 2.2% fewer services per patient per quarter than their male colleagues (p < 0.01). In two specialties differences between women aged 40 years or less and those over 40 years were observed. In general internal medicine the younger women had higher activity levels than the older women (p < 0.01). Conversely, in dermatology the younger women had lower activity levels (p < 0.05) and provided fewer services per patient per quarter (p < 0.001) than the older women.ConclusionsAlthough physician's sex explained much of the variation in activity level and service intensity, even after other important correlates were controlled for, the type and extent of differences observed between female and male physicians depended on the particular medical field examined. To understand the effect of the large increase in the number of women on the physician workforce, more detailed analyses by medical field are needed of the volume, mix and intensity of services provided by men and women, with adjustment for any possible differences in the patients seen in their practices.

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