A total of 693 children between the ages of 0 and 13 years were randomly assigned to either a staff model HMO or to one of several fee-for-service insurance plans in Seattle to evaluate differences in medical expenditures and health outcomes. Although the fee-for-service plans varied the amount of cost sharing (0% to 95%), all children were covered for the same medical services, for either 3 or 5 years. No differences in imputed total expenditures were observed for children assigned to the HMO or any of the fee-for-service plans. Children with cost-sharing fee-for-service plans, however, had fewer medical contacts and received fewer preventive services than those assigned to the HMO. Nonetheless, children with the cost-sharing fee-for-service plans were perceived (by their mothers) to be in better health overall than those assigned to the HMO. No significant differences regarding physiological outcomes (eg, visual acuity, hemoglobin level) were observed between the two groups. The results of this experiment neither strongly support nor indict fee-for-service or prepaid care for children.

To determine whether health outcomes in a health maintenance organisation (HMO) differed from those in the fee-for-service (FFS) system, 1673 individuals ages 14 to 61 were randomly assigned to one HMO or to an FFS insurance plan in Seattle, Washington for 3 or 5 years. For non-poor individuals assigned to the HMO who were initially in good health there were no adverse effects. Health outcomes in the two systems of care differed for high and low income individuals who began the experiment with health problems. For the high income initially sick group, the HMO produced significant improvements in cholesterol levels and in general health ratings by comparison with free FFS care. The low income initially sick group assigned to the HMO reported significantly more bed-days per year due to poor health and more serious symptoms than those assigned free FFS care, and a greater risk of dying by comparison with pay FFS plans.

Do children whose families bear a percentage of their health care costs reduce their use of ambulatory care compared with those families who receive free care? If so, does the reduction affect their health? To answer these questions, 1,844 children aged 0 to 13 years were randomly assigned (for a period of 3 or 5 years) to one of 14 insurance plans. The plans differed in the percentage of their medical bills that families paid. One plan provided free care. The others required up to 95% coinsurance subject to a +1,000 maximum. Children whose families paid a percentage of costs reduced use by up to one third. For the typical child in the study, this reduction caused no significant difference in either parental perceptions of their child's health or in physiologic measures of health. Confidence intervals are sufficiently narrow for most measures to rule out the possibility that large true differences went undetected. Nor were statistically significant differences observed for children at risk of disease. Wider confidence intervals for these comparisons, however, mean that clinically meaningful differences, if present, could have been undetected in certain subgroups.