But there’s one crucial detail we don’t have much information on at all: what those 34 million people will do with their health insurance once they get it. And it’s actually a pretty open question in the health policy research, whether the newly-insured use more health services (making up for the earlier lack of coverage) or continue to act as they did prior to gaining coverage.

The latest research says it looks more like the latter: the newly-insured tend to act more like the uninsured, according to a study published earlier this week in the journal Health Economics (hat tip: the Incidental Economist). The study looked at Medicare enrollees, comparing newly-qualified seniors who had health insurance before turning 65, versus those who did not. It finds that those who did not have insurance had 11 percent fewer doctors visits than those who had insurance prior to gaining Medicare coverage.

Interestingly though, this study didn’t find a cost difference between these two populations. Even though the previously-uninsured got less medical care, they gravitated to more expensive treatments, with 18 percent more visits to the emergency room and 43 percent more hospital outpatient trips.

These numbers are bad news for our attempt to control health cost growth. The health reform law’s insurance expansion is largely meant to encourage greater preventive care, to curtail the more expensive hospital and emergency room treatments. If it doesn’t - and our patterns of care look pretty similar to what we have now - we’re in some trouble.

What this means for implementation, I think, is that any public outreach campaigns on the health insurance expansion will have to do more than get Americans enrolled. It will have to do a pretty good job explaining what it means to have health insurance, and how to use it. Or, as the study authors put it, “both health insurance coverage and other policies that facilitate access to physician services among the previously uninsured may be necessary to substantially alter their use of health care.”