In their analysis of HSAs, authors Remler, a professor at the Baruch College School of Public Affairs, City University of New York, and Glied, chair of the Department of Health Policy and Management at Columbia University, compared HSAs combined with high deductible plans with traditional health insurance policies. They found that the 7.7 percent of people who are responsible for half of all medical spending would see no change or a decrease in their level of cost-sharing under an HSA/high-deductible plan.

In contrast, cost-sharing would increase for people who spend between $700 and $6,100 of their own money on health care. Taking the tax subsidies of HSAs into account, the authors found that for enrollees with a 40 percent marginal tax rate (including exclusion of HSA contributions from both income and payroll taxes), only those with expenses between $700 and $2,500 would see an increase in the marginal and average cost-sharing.

"Health care spending is highly concentrated among a small group of people who have very high medical costs," said Remler. "This study shows that a high-deductible HSA would have no effect on this spending, leaving a negligible impact on health care costs."

Out-of-pocket caps in HSA-eligible high deductible health plans are a primary reason why cost-sharing decreases rather than increases. For example, once a person with a typical high-deductible health plan (no coinsurance, a deductible of $2,500 and an out-of-pocket maximum of $2,500) spends $2,500 there are no additional out-of-pockets costs. However, in a traditional plan with no deductible but a 20 percent coinsurance, a person would have to spend $12,500 before they would reach their maximum out-of-pocket costs.; Source: Commonwealth Fund