Hi, friend! May I ask why should evaluators need to make sure comparison practices are as similar as possible to intervention practices before the intervention begins?

Not at all.

Thank you so much.

If the intervention and comparison groups are similar before the intervention begins, you can be more confident that the intervention caused any subsequent differences in outcomes between the two groups. If available, your evaluation should select comparison practices with similar patient panels, including age, gender, and race; insurance source; chronic conditions; and prior expenditures and use of hospitalizations, ER visits, and skilled nursing facility stays. Ideally, practice-level variables such as practice size; whether the practice is independent or part of a larger system; the number, types, and roles of nonphysician staff; and urban/rural location should also be similar. To improve confidence further, if data are available, you should examine how similar outcomes were in both groups for several years before the intervention began to ensure patients in the two groups had a similar trajectory of costs. Moreover, if there are preexisting differences in cost trends, you can control for them. You can examine the comparability of the intervention and comparison practices along as many of these dimensions as possible even if you cannot use all of them to select the comparison group.