Randomized clinical trials do not require representative patients; they require representative treatment effects. Generalizability of randomized trial findings for relative efficacy comes from one of three things: (1) true absence of interactions, (2) interacting factors have a similar distribution in the RCT as in the target population, or (3) the RCT sample has enough representation of the distribution of interacting factors to allow them to be modeled and used to estimate treatment effects in target patients, and the researcher knows to include these interactions in her model. — Implications of Interactions in Treatment Comparisons