It chose what was a novel solution for the time. It dropped its standard deal — a subsidy that rose in line with the price of the insurance policy — and switched some 10,000 workers on its payroll to a fixed subsidy that encouraged them to shop around for care.

For Harvard’s accountants, the change worked wonders. A study a couple of years later by David M. Cutler, a Harvard economist, and Sarah Reber, a Harvard graduate, concluded that competition among insurers cut the university’s health bill by 5 to 8 percent.

But not everybody was equally pleased. Families of workers who chose the Preferred Provider Organization offered by Blue Cross/Blue Shield — the most comprehensive plan, with lots of doctors and hospitals on its network — faced a $500-a-year jump in their out-of-pocket spending on health care.

Younger and healthier workers canceled their P.P.O. plans, enrolling in cheaper H.M.O. options or dropping Harvard insurance altogether. Left with a sicker patient base, the P.P.O. raised its premiums further, which prompted the next layer of relatively healthy customers to leave.

And so on. In 1997, Blue Cross/Blue Shield withdrew its P.P.O. from the market, making it a victim of what economists call the death spiral of adverse selection.

In a couple of months the nation is set to experience a similar shock on a very large scale: the greatest change in how Americans pay for health care since the advent of Medicare nearly half a century ago.

Come October, millions of uninsured people will be able to choose one of several health plans, offered at four different tiers of service and cost through new health exchanges coming onstream in every state.

Cheap “bronze” plans will shoulder some 60 percent of patients’ medical expenses. Pricey “platinum” plans will cover at least 90 percent. But insurers will not be allowed to exclude people with pre-existing conditions, or charge more for the sick, or put a lifetime cap on medical costs. Their policies will have to cover a minimum standard of medical care. And the government will subsidize those who cannot afford to buy the policies.

President Obama and his advisers hope the overhaul will do two things. The first is to extend coverage to tens of millions of Americans who today lack health insurance. The second is to hold the line on rising health care costs.

“Over time, success will depend on what happens to the cost curve,” Professor Cutler told me. “If we don’t bend the cost curve, everything will fail. The government won’t be able to afford it. Nobody will be able to afford it.”

In theory, the overhaul could meet both goals. Millions of new Americans armed with a subsidy and shopping among plans would bring consumer choice to bear, finally, on the health care industry. Insurers would compete to create policies that offered the most value for money, pressuring hospitals and doctors on behalf of all of us.

Yet despite the care the administration took in establishing incentives and safeguards, even some of Obamacare’s most committed backers are wondering whether the experiment will work as advertised — or, like Harvard’s P.P.O., go off the rails along the way.

Adverse selection is perhaps the direst threat. For Obamacare to work, millions of healthy, young, uninsured Americans must join a health plan to counterbalance the sicker millions who are most likely to buy insurance. Otherwise, health plans on the exchanges will have to raise premiums to shoulder the higher costs.

Selection will also take other forms. Healthier Americans will probably flock to cheaper bronze plans. And insurers will vie to enroll the healthy. In some states, big insurers have chosen not to participate in exchanges to avoid their strictures. On the outside, they could still sell cheap plans to skim off the healthy and avoid a rule that insurers on the exchanges must also offer more generous silver and gold plans.

Adverse selection is not the only risk.

A few studies have found that more competition among health insurers leads to lower hospital fees on average and that premiums rise when insurer competition diminishes. But researchers have also found that top hospitals — which any decent plan must have on its network — increase their fees when more health plans compete for their business.

E-mail: eporter@nytimes.com; Twitter: @portereduardo

Article source: http://www.nytimes.com/2013/08/08/business/economy/for-obamacare-some-hurdles-still-ahead.html?partner=rss&emc=rss