Balancing the strengths of systematic and narrative reviews

Abstract

1Department of Obstetrics and Gynecology, McMaster University, Hamilton, Ontario, 2Department of Obstetrics and Gynaecology, Dalhousie University, Halifax, Nova Scotia, Canada and 3Department of Reproductive Medicine, University Medical Center, Utrecht, The Netherlands The mandate of Human Reproduction Update involves several roles: (i) to provide a synthesis of evidence that can aid scientists and clinicians in their daily work; (ii) to help reproductive specialists understand concepts from related disciplines; and (iii) to summarize current knowledge generated by basic science as the foundation of future scientific and clinical advancement. Given that review and synthesis are central to good scientific and clinical practice, and that a grasp of the current state of knowledge is a prerequisite to designing new studies, it is pertinent to ask which reviews are most likely to fulfil the needs of readers. A related question concerns whether systematic reviews meet the needs of all review topics and all readers. Summarizing evidence or knowledge is a difficult problem in reproductive medicine, as in other branches of science and medical care (Eddy et al., 1992). For each question there may be multiple studies that use different designs and inclusion criteria. For clinical questions, the interventions, outcomes and measures of effect may vary: the effect measures in treatment studies include odds ratios, relative risks and absolute differences. For scientific questions, the experimental species, models and designs may differ. Moreover, it is always uncertain whether all of the relevant evidence has been evaluated. Even when the search has been exhaustive, there are no simple guides on how to interpret conflicting results and whether to accept apparently outlying studies. The choices that the reviewer makes to address the variable conditions and uncertainties may be conservative, strict and exclusive, or liberal, open and inclusive. The decisions made by the reviewer may not be consistent throughout and these choices may or may not satisfy the reader who seeks out the review to address a clinical or research question. Faced with uncertainty and doubt, readers nonetheless must form an impression of the evidence and synthesize the state of knowledge in order to address the clinical or research question that stimulated their interest in the review. We argue that the reader is better served when the choices made in the review, regardless of whether they are strict or open, should be explicit, transparent, clearly stated and reproducible by interested readers.