Nelson Systematic Reviews to Answer Healthcare, Questions, 2e


Chapter 6 • Selecting Studies for Inclusion

■ ■ SUMMARY • There are numerous ways to introduce reviewer bias and random error during the selection of studies for a systematic review. Clear and objective prespecified eligibility criteria and a transparent and well-documented process help users of the review understand the inclusion decisions, their implications for the review’s findings, and their impact on applicability. • Eligibility criteria should be comprehensive, but not all scenarios can be anticipated and refinements are likely. Piloting the criteria with a subset of publications is recommended to identify and resolve initially unrecognized issues. • Study selection usually involves a two-stage process: screening titles and abstracts to effi ciently eliminate all obviously ineligible publications; followed by assessing details of the subset of full-text publications that were determined to be likely or possibly eligible based on the initial screen. • Two or more independent reviewers should screen and select publications for inclusion, using a consensus process to refine criteria and make final decisions about inclusion. • Reviewers are encouraged to use coding systems during the study selection process to keep track of the inclusion decisions for each publication. • Literature flow diagrams, such as the PRISMA template, are recommended to report the results of the study selection process. These diagrams include the numbers of overall pub lications identified; publications excluded based on screening titles and abstracts; full-text publications retrieved; full-text publications excluded and reasons for exclusion; and studies included in the systematic review. The systematic review of the effectiveness of patient navigation to increase cancer screening in populations adversely affected by health disparities described in Box 6.1 encountered additional questions in selecting studies for inclusion at the full-text review stage of the review process. • Studies varied by whether they enrolled patients with previous screening experiences includ ing: only patients who had never been previously screened for cancer; only patients who had been previously screened; or both previously screened and nonscreened patients. 1. What are the implications of including studies enrolling these different groups of patients? 2. Should the systematic reviewers refine their inclusion criteria? If so, how? • Older studies of colorectal cancer screening eligible for the systematic review used proce dures that are no longer preferred for screening (sigmoidoscopy and barium enema). CASE STUDY: Refining Eligibility Criteria for a Systematic Review of the Effectiveness of Patient Navigation to Increase Cancer Screening

3. What are the pros and cons of including studies using older technologies? 4. Should the systematic reviewers refine their inclusion criteria? If so, how?

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The author would like to acknowledge the contributors to the first edition: Marian S. McDonagh and Kim Peterson.

REFERENCES 1. Institute of Medicine. Finding What Works in Health Care: Standards for Systematic Reviews . Washington, DC: The National Academies Press; 2011. 2. Cook DJ, Reeve BK, Guyatt GH, et al. Stress ulcer prophylaxis in critically ill patients. Resolving discordant meta-analyses. JAMA . 1996;275(4):308–314. 3. Hopayian K, Mugford M. Conflicting conclusions from two systematic reviews of epidural steroid injections for sciatica: which evidence should general practitioners heed? Br J Gen Pract . 1999;49(438):57–61.

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