In the health care frenzy, one letter from the Government Accountability Office has managed to pass nearly unnoticed. Perhaps it’s because the definitive piece of news it provides seems completely obvious: More competition in the health care industry means lower costs for consumers.

Addressed to Senator Herb Kohl, chairman of the Subcommittee on Antitrust, Competition Policy and Consumer Rights, the letter details the GAO’s findings on competition in the health insurance industry. The office surveyed 41 studies conducted from 1990 to March 2009, in search of papers on market concentration in relation to premium rates, quality of care, efficiency and insurer profit.

The verdict? Hung jury. Under most subjects, the GAO admits, results were mixed. Take efficiency: “Several studies found that less competition was associated with greater cost savings for insurers or hospitals,” the letter observes, “although another study we reviewed found the opposite relationship.”

This is partly because, the letter’s authors point out, much of the data they found relied on state or national-level data, “when the more appropriate geographic focus may be at a more local level. One study found that the HMO industry became more consolidated nationally from 1994 to 1997 … the effects of these national consolidations on concentration varied significantly, with some local markets experiencing no change and others facing increases significant enough to raise antitrust concerns.”

“We tried to link different studies to different categories of reviews,” explained John Dicken, director of the GAO’s health care division. “Everything was attempting to control [for variables] … but it’s really hard to compare across different studies.”

The category most scrutinized turned out to be quality of care–15 of the 41 studies examined competition’s effect on this aspect (the study of efficiency came in second, with eight papers). It was also the most contentious–one study found market competition ran with poorer performance in women’s care and customer satisfaction, while another found that competition increased the likelihood that patients would be assigned a primary care physician, thus improving the quality of care. Another study found no correlation at all.

If anything, the GAO paper highlights the need for more reliable and accountable information from the health care industry. As Dicken pointed out, most of the studies centered on HMOs, since they couldn’t find reliable information concerning PPOs. Comparing different geographic scopes seriously complicated matters. “Ideally,” Dicken said, “you’d want data at the local markets level.”

No word yet from how Sen. Kohl’s subcommittee will be utilizing the data, given all the curve balls the GAO fielded. But the study did find one area of relatively unambiguous agreement: Competition in a given market led to lower premiums for patients–and fewer profits for insurance companies.

Granted, some opponents of health care reform likely already know this, as they’ve accused the government of pushing them out of the business. President Obama has pointed out, on multiple occasions, that competition is supposed to be a positive force in the industry. Meg White over at BuzzFlash snarks, “I doubt this document will make much of an impression on the other side of the aisle. It seems Republicans feel truly free market competition is only good when it applies to arguments for deregulation, not actually breaking up monopolies.”