In the RAND Health Insurance Experiment (HIE), cost-sharing reduced the probability of using medical care across a wide spectrum of individual conditions and reasons for seeking care, perhaps somewhat more for acute illnesses and preventive care than for chronic disease. It had equivalent effects in curtailing use of highly effective and only rarely effective medical care, suggesting that it did not have an especially selective impact. Finally, it influenced care-seeking behaviors for persons of low income more than for persons of greater means, and it especially deterred the use of medical care by poor children. In interpreting these findings on the use of ambulatory care in the context of previously reported health status results from the HIE, this report, which originally appeared in Medical Care, v. 24, no. 9, Sept. 1986, suggests that one way to explain why so few adverse effects of cost-sharing were detected may be certain offsetting effects of the additional services received by persons with free care: i.e., at the margin, the negative effects of unnecessary or inappropriate care tend to balance the beneficial effects of appropriate care. This supposition leads the authors to consider several research and policy implications in the areas of measuring patient outcomes, improving the nature and dissemination of information to patients, improving quality-of-care assessment and assurance techniques, and assessing several health care financing options for the disadvantaged.

Health care expenditures of 1,136 children whose families participated in a randomized trial, The Rand Health Insurance Experiment, are reported. Children whose families were assigned to receive 100% reimbursement for health costs spent one third more per capita than children whose families paid 95% of medical expenses up to a family maximum. Outpatient use decreased as cost-sharing rose for a variety of use measures: the probability of seeing a doctor, annual expenditures, number of visits per year, and numbers of outpatient treatment episodes. Hospital expenditures did not vary significantly among children insured with varying levels of cost-sharing. Episodes of treatment for preventive care were as responsive to cost-sharing as episodes for acute or chronic illness. The results give no reason not to insure preventive care as liberally as care for acute illness.

This report, a shorter version of which appeared in the May 1985 issue of Pediatrics, considers how cost sharing affects the use of medical care by children under age 14. The authors draw upon data collected during the RAND Health Insurance Experiment to examine total expenditures on medical care and hospital and outpatient use, particularly the use of preventive services. Results indicate that per capita use of medical services was one-third greater for children whose families were assigned to a health plan that reimbursed them completely for medical services than for children whose families paid 95 percent of medical expenses. Outpatient services decreased as cost sharing rose for a variety of measures: the probability of seeing a doctor during the year, total annual expenditures, and number of visits per year. These results imply that reducing the amount of cost sharing for pediatric care will lead to substantial increases in outpatient use. However, reducing coinsurance for children's hospital expenses can be expected to have little impact on total costs of medical care.