Background: Ambulatory Care Groups (ACGs), a US case-mix system that uses the patient as the unit of analysis, is particularly appropriate for health care systems in which physicians serve a defined list of patients.
Objective: To determine the extent to which the categorization of patients according to ACGs would account for the utilization of primary care services in a national health care system within the European Union.
Methods: Of all subjects continuously assigned to 9 physicians from public primary health care centers in Bizkaia, Basque Country (Spain) over a 12-month period, those visited at least once (n = 9,093) were included. According to the subject's age, sex, and ICD-9-CM diagnoses assigned during a year of patient-provider encounters, patients were classified by means of the ACGs system.
Results: Multiple linear regression analyses indicated that age and sex did not explain more than 7.1% of the variance in annual visits made by adults and 25.7% by children to primary care physicians. However, the r2 adjusted to the ACGs model was 50% and 48%, respectively, and even higher, that is 58% and 64% for another component of the system, the Ambulatory Diagnostic Groups (ADGs).
Conclusions: Those results support the inadequacy of using the patient's age and sex alone to estimate physicians' workload in the primary health setting and the need to consider morbidity categories. The ACGs case-mix system is a useful tool for incorporating patients' morbidity in the explanation of the use of primary health care services in a European national health system.