In seeking the evidence on which to base clinical practice, we are faced with myriad published papers and websites, often offering unclear or conflicting information regarding the choice of interventions, diagnostic tools, or expectations of outcomes. We also face the need to critically appraise these studies to determine how well they support clinical decisions—a potentially overwhelming task when the number of studies is large (see Chapter 36). Any single study, even if well-designed, is essentially a form of tentative evidence, which needs confirmation by additional research. Therefore, researchers and practitioners benefit from syntheses of literature that summarize and critique published studies.
Systematic reviews present comprehensive information regarding findings from several sources with an analysis of the methodological quality of the studies. Reviews can be extended by pooling data from several studies in a process of meta-analysis, which presents collective statistical measures of effect size. A more recent contribution to synthesis is the scoping review, which is a broader and less structured approach that offers assessment of emerging evidence.
The purpose of this chapter is to describe the process of synthesizing literature, how reviews are developed and written, and how data can be presented and interpreted. Because searching for published studies is an important part of synthesis, reviewing the content in Chapter 6 will be useful.
Purpose of Systematic Reviews
Systematic reviews are a form of research using a rigorous process of searching, appraising, and summarizing existing information on a selected topic. The procedures for conducting the review are intended to be inclusive of the body of research evidence at the time the review is undertaken. Varied types of reviews can serve different purposes (see Table 37-1). Reviews are most commonly focused on the effectiveness of interventions but can be used to address the accuracy of diagnostic and measurement tools, to identify prognostic or risk factors, and to develop recommendations for clinical practice guidelines.1,2 Results provide a structured approach to examining data to inform practitioners in their decisions to maintain, alter, or discard methods of clinical practice and to aid researchers in designing further research.
Table 37-1Types of Evidence Synthesis |Favorite Table|Download (.pdf) Table 37-1 Types of Evidence Synthesis
|SYSTEMATIC REVIEWS/META-ANALYSES |
|Systematic Review ||A summary of the medical literature that uses explicit methods to perform a thorough literature search and critical appraisal of individual studies. |
|Meta-Analysis ||A statistical technique to pool results of valid studies within a systematic review. Analysis of intervention studies involves differences between treatment and comparison intervention. Analysis of diagnostic or prognostic factors can include risk estimates. |
|Overview ||A systematic review that synthesizes systematic reviews on the same topic. Does not appraise individual trials.8 |
|Network Meta-Analysis ||A systematic review with meta-analysis that assesses ...|