Differences in the mix of patients among medical specialties and systems of care. Results from the medical outcomes study.

OBJECTIVE To determine differences in the mix of patients among medical specialties and among organizational systems of care. STUDY DESIGN Cross-sectional analysis of 20,158 adults (greater than or equal to 18 years of age) who visited providers' offices during 9-day screening periods in 1986. Patient and physician information was obtained by self-administered, standardized questionnaires. SETTING Offices of 349 physicians practicing family medicine, internal medicine, endocrinology, and cardiology within health maintenance organizations, large multispecialty groups, and solo or small single-specialty group practices in three major US cities. OUTCOME MEASURES Demographic characteristics, prevalence of chronic disease, disease-specific severity of illness, and functional status and well-being. RESULTS Among patients with selected physician-reported chronic illnesses (diabetes, hypertension, recent myocardial infarction, or congestive heart failure), increasing levels of severity were associated with decreasing levels of functional status and well-being and with increased hospitalizations, more physician visits, and higher numbers of prescription drugs. Compared with patients of general internists, patients of cardiologists were older (56 vs 47 years, P less than .01), had worse functional status and well-being scores (P less than .01), and carried more chronic diagnoses (mean 1.32 vs 1.02, P less than .01); patients of family practitioners were younger (40 vs 47 years, P less than .01) and more functional (P less than .01), carried fewer chronic diagnoses (0.70 vs 1.02, P less than .01), and (among diabetic patients only) had lower disease-specific severity scores (2.06 vs 2.30 on a five-point scale, P less than .01). Compared with patients in health maintenance organizations, patients visiting solo practitioners under fee-for-service payment were older (50 vs 45 years, P less than .01) and sicker (had worse physical functioning) and had a higher mean number of chronic diagnoses (1.10 vs 0.93, P less than .01). CONCLUSION Patient mix is related to utilization and differs significantly across medical specialties and systems of care. These differences must be taken into account when interpreting variations in utilization and outcomes across specialties and systems, and when considering alternative policies for payment.