Nelson Systematic Reviews to Answer Healthcare, Questions, 2e


Selecting Studies for Inclusion

Amy G. Cantor

■ ■ INTRODUCTION As described in the previous chapter, a sufficiently comprehensive and objective literature search ensures the identification of as many potentially relevant studies as possible. However, only a fraction of the studies identified by the literature search will ultimately be included in a systematic review. The process for selecting studies is critical to the systematic review, as it shapes the overall body of evidence upon which all conclusions will be drawn. Decisions about selecting studies are based on whether they meet prespecified inclusion and exclusion criteria that represent the specific populations, interventions, comparators, outcomes, timing, settings, and study designs of interest (PICOTS). However, these decisions involve reviewer judgment that is inherently subject to variation and random error depending on interpreta tion, experience, and expertise. Care must be taken throughout the study selection process to minimize bias. Several standards provide guidance for the screening and selection of studies (Table 6.1). 1 This chapter describes accepted procedures for study selection, how to docu ment the selection process, and important issues to consider when applying inclusion and exclusion criteria. TABLE 6.1 STANDARDS FOR SCREENING AND SELECTING STUDIES SCREEN AND SELECT STUDIES • Include or exclude studies based on the protocol’s prespecified criteria • Use observational studies in addition to randomized clinical trials to evaluate harms of interventions • Use two or more members of the review team, working independently, to screen and select studies • Train screeners using written documentation; test and retest screeners to improve accuracy and consistency • Use one of two strategies to select studies: read all full-text articles identified in the search or screen titles and abstracts of all articles and then read the full-text of articles identified in initial screening • Taking account of the risk of bias, consider using observational studies to address gaps in the evidence from randomized clinical trials on the benefits of interventions DOCUMENT THE SEARCH • Provide a line-by-line description of the search strategy, including the date of search for each database, web browser, etc. • Document the disposition of each report identified including reasons for their exclusion if appropriate Source: Institute of Medicine. Finding What Works in Health Care: Standards for Systematic Reviews . Washington, DC: The National Academies Press; 2011. Reprinted with permission from the National Academies Press, Copyright 2011, National Academy of Sciences.

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