Reviews: Making Sense of an Often Tangled Skein of Evidence

Medical science is an intricately detailed tapestry of evidence, woven over many decades, from tens of thousands of hypotheses and observations. Astute observers rarely discern the tapestry's pattern from single studies; they know that a single study seldom allows people to see a pattern that changes insight and clinical practice. Far more often, medical practice changes only after a body of evidence accumulates to the point of revealing meaningful patterns. Recognizing the central role of evidence synthesis in shaping standards for clinical practice, Annals places a high priority on publishing up-to-date summative articles. This editorial offers advice for review artisans who hope to see their wares on display in Annals. In an accompanying supplement sponsored by the Agency for Healthcare Research and Quality (part 2 of this issue), authors from the North American Evidence-based Practice Centers offer detailed advice on how to do systematic reviews, how to compile evidence reports, and how to handle the many methodologic challenges involved in writing systematic reviews.

Reviews that appear in Annals are either systematic or narrative. Systematic reviews usually address a small number of focused questions and use rigorous, structured methods to search, select, evaluate, and synthesize the existing evidence to answer these questions. Some systematic reviews use meta-analysis to combine the findings of individual studies to estimate the true relationships between the exposures or interventions and outcomes of interest. The accompanying supplement further defines systematic reviews.

Narrative reviews are more difficult to define, but we know one when we …