Measuring how use of the medical home concept affects quality, cost and patient experience has been problematic and, in a new Decisionmaker Brief titled “Improving Evaluations of the Medical Home,” the U.S. Agency for Healthcare Research and Quality provides guidance into how to structure research to establish and refine the value of operating a practice as a patient-centered medical home.

By definition, medical homes provide patient-centered, comprehensive and coordinated care with increased patient access and a commitment to quality and safety improvement. In the brief, it's noted that it's unknown how well current medical homes are achieving quality, cost and experience goals because much of the research has been done without a control group for comparison or does not adjust for “clustering.”

The brief defined clustering as patient outcomes that are more similar within a practice than to patient outcomes in other practices. Failure to adjust for clustering ignores “systematic differences between the practices,” according to the brief.

According to an accompanying white paper, “Building the Evidence Base for the Medical Home: What Sample and Sample Size Do Studies Need?” ignoring clustering creates false positives. And, in the brief, it's stated that “the likelihood of concluding that an intervention works when it does not can be very large.”

The brief ranks as “poor” the evidence coming from studies that show data before and after an intervention from a single practice. It goes on to explain that, for stronger evidence, it is better that studies include data from fewer patients but from more practices. According to the white paper, “a study with 100 practices and 20 patients per practice has much greater power than a study of 20 practices with 100 patients each.”

The brief emphasizes that, for proper study structuring, it must be recognized that—when investigating the effects of transforming the practice into a patient-centered medical home—the practice itself “is the unit of intervention” and not the individual patients.

“It is not feasible, perhaps not even possible, to deliver most components of PCMH-type care to only some patients within a primary care practice,” according to the brief.