HMOs' savings have 'spillover effect'--studies.

Researchers are gathering evidence that as health maintenance organizations increase market share, they act as a brake on a community's rising medical costs. In other words, competitive pressures from HMOs have a 'spillover effect' on the free-for-service sector, according to the author of one study. Meanwhile, a study of hospitals in California attributed more than $1 billion in savings in one year to the influence of HMOs on the market.