A Call for Systematic Reviews

In this editorial, we discuss the power of systematic reviews and their central role in evidence-based practice, and we encourage authors of systematic reviews to submit them for publication in Journal of General Internal Medicine . Most clinical care research studies enroll patients who represent only a narrow spectrum of those to whom clinicians may wish to apply the results. 1 Also, most studies are not large enough on their own to measure precisely all relevant patient-important outcomes, for instance, both benefits and harms of therapy. Small studies often produce indeterminate or contradictory results. One potential solution is to conduct large clinical studies enrolling a wide variety of patients and measuring all patient-important outcomes with precision. 2 An alternative is to summarize and synthesize existing evidence in a systematic review. In contrast to a nonsystematic review (i.e., the majority of narrative reviews and book chapters), a systematic review typically allows readers to appraise how the review was conducted and the evidence synthesized. Rather than being all encompassing, systematic reviews focus on a single question or a small set of closely related questions. In offering an answer, reviewers might decide to pool the results of individual studies using statistical techniques, a procedure called meta-analysis. Not all systematic reviews allow for such pooling. Also, not all meta-analyses pool the results of studies identified systematically. In this communication, we refer to both systematic reviews and to the meta-analyses conducted across studies included in systematic reviews. Clinicians can trust the validity of a systematic review to the extent that it was conducted rigorously using protocols to implement safeguards against bias in assembling, critically appraising, and synthesizing the evidence. Highquality reviews also systematically explore and explain between-study differences. Such systematic reviews may yield valid, precise, and widely applicable answers to focused clinical questions. 3 Thus, systematic reviews have come to play a central role in 1) informing clinical decisions and guidelines and 2) identifying knowledge gaps for researchers and funding agencies. Because of their power to aid both clinicians and researchers, JGIM encourages authors of systematic reviews to submit them for publication in our journal. The idea of systematically synthesizing research evidence began to emerge in the 18th and 19th centuries. In their historical account of evidence synthesis, Chalmers, Hedges, and Cooper noted that work published as early as 1904 in England and 1907 in the United States shared features with modern meta-analyses. 4 Meta-analytic techniques evolved and matured in agriculture and the social sciences and preceded the identification of mechanisms to prevent bias in research synthesis. It was in the late 1980s and early 1990s that research documented the shortcomings of narrative reviews (and of the recommendations included in them). 5–7 Consequently, the number of systematic reviews and meta-analyses increased, and methodologists published criteria by which the quality of a systematic review could be judged. 8,9