AMBULATORY CARE PRACTICE VARIATION WITHIN A MEDICAID PROGRAM

Study Questions. What is the extent of variation in patterns of ambula tory care practice across one state's Medicaid program once case mix i s controlled for? How much of this variation in resource consumption i s explained by factors linked to the provider, patient, and geographic subarea? Data Sources/Study Setting. Practices of all providers deliv ering care to persons who were continuously enrolled in the Maryland M edicaid program during FY 1988 were studied. A computerized summary of all services received during this year for 134,725 persons was develo ped using claims data. We also obtained data from the state's benefici ary and provider files and the American Medical Association's masterfi le. Each patient was assigned to a ''usual source of care'' (primary p rovider) based on the actual patterns of service. The Ambulatory Care Group (ACG) measure was used to help control for case mix. Study Desig n. This was a cross-sectional study based on the universe of continuou sly enrolled Medicaid enrollees in one state. Principal Findings. Afte r controlling for case mix, the variation in patient resource use by t ype of primary provider was 19 percent for ambulatory visits, 46 perce nt for ancillary testing, 61 percent for prescriptions, and 81 percent for hospitalizations. Across Maryland counties, comparing the low- to high-use jurisdiction, there was 41 percent variation in case mix-adj usted visit rates, 72 percent variation in pharmacy use, and 325 perce nt variation in hospital days. At the individual practice level, physi cian characteristics explain up to 17 percent of ambulatory resource u se and geographic area explains only a few percent, while patient char acteristics explain up to 60 percent of variation. Conclusions. Since a large proportion of variation was explained by patient case mix, it is evident that risk adjustment is essential for these types of analys es. However, even after adjustment, resource use varies considerably a cross types of ambulatory care provider and region, with consequent im plications for efficiency of health services delivery.