An unprecedented behind-the-scenes look at the prices that majorinsurers pay for medical services presents a serious challenge toprevailing beliefs about how to lower health care costs.

For years, experts have argued that hospital mergers can play animportant role in driving down medical spending. Their evidence wasdata on Medicare spending around the country. President Obama evenhighlighted exceptionally low Medicare spending costs in GrandJunction, Colorado as an example of a health system that coulddeliver better prices to consumers.

But new data shows that what consumers and insurers are spendingin the private market in a given area doesn’t necessarily alignwith Medicare spending. Grand Junction, for instance, hashigher-than-average private sector health costs. While the area’slarge hospitals may drive down Medicare spending by avoidingduplicative costs, according to the New York Times, they oftenforce insurers in the private market to pay more for proceduresbecause of the bargaining power they gain from their size and lackof competition.