We restricted our cohort to systematic reviews of randomized trials of conventional drugs, devices, or procedures that reported meta-analytic results for at least 1 dichotomous outcome. Our exclusion of qualitative reviews, reviews of nontherapeutic topics, meta-analyses of individual-patient data, and meta-regressions reflected our concern that rates of change in evidence might differ across these different types of reviews. Thus, we acknowledge that our results may not generalize to all reviews. That said, as shown in Appendix Figure 1, excluding the records retrieved by our initial electronic search that were not systematic reviews, 139 of the first 287 systematic reviews (48%) were eligible for inclusion. Thus, although our cohort may seem highly selected, approximately half of the reviews indexed in ACP Journal Club were eligible for inclusion in our cohort. Granted, ACP Journal Club itself represents a nonrandom sample of all systematic reviews insofar as it selects reviews that meet certain quality standards and have high potential to affect clinical practice. However, these biases strengthen our results because such reviews represent those one would hope to have the greatest stability.