“…Interestingly, the little endogenous critical literature on enriched enrollment takes issue not with its limited external validity, but with the claims to improved internal validity. Several authors have noted that the use of a run-in phase prior to randomization, which familiarizes all participants with a drug's effects, presents a risk for unblinding (Leber and Davis, 1998;Staud and Price, 2008a, b;Furlan et al, 2011;Hall and Kaptchuk, 2013). In addition, a recent meta-analysis comparing enriched with non-enriched trials for opioids in chronic non-cancer pain found that contrary to its rationale, EERW studies did not appear to produce stronger measures of efficacy, but tended to underestimate adverse events, which, as we will explore below, has a particular salience for studies of chronic pain treatments (Furlan et al, 2011;Quessy, 2011).…”