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Systematic Reviews: Introduction

 According to the Cochrane Handbook for Systematic Reviews of Interventions, a systematic review attempts to gather all empirical evidence that fits pre-specified criteria in order to answer a specific research question. A systematic review has: 1) a clearly stated set of objectives with pre-defined eligibility criteria for studies; 2) an explicit, reproducible methodology; 3) a thorough, objective and reproducible search of a range of sources to identify as many relevant studies as possible; 4) an assessment of the validity of the findings for the included studies; 5) a systematic presentation and synthesis of the characteristics and findings of the studies.

Source: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.0 (updated July 2019). Cochrane, 2019. Available from

The Systematic Review Process

  1. Define your research question.
  2. Determine that there are no existing systematic reviews or systematic review protocols that address your question.
  3. Assemble your research team. The team should ideally include subject area specialists, a specialist versed in systematic review methods and a librarian/information specialist who has had training in systematic review methods.
  4. Develop your protocol, which is a detailed description of the objectives and methods of the review. It should include the rationale and objectives of the review, the inclusion/exclusion of the criteria, methods for locating studies, quality assessment methods, data extraction methods, data synthesis methods,etc.
  5. Register your protocol.
  6. Review the literature to search for studies.
  7. Screen titles and abstracts to identify potentially relevant studies.
  8. Review full-text and apply inclusion and exclusion criteria.
  9. Assess quality of eligible studies.
  10. Depending on the type of review, extract data from individual studies.
  11. Analyze data and synthesize if appropriate.
  12. Report findings.

Is there already a systematic review on your topic?

Use the resources listed below to see if a review on your topic is currently in progress or has already been published by someone else. If a review already exists, is it in need of updating or is it a poor quality review? If so, consider whether an update is in order, or whether a new systematic review should be performed.

  • Cochrane Library is the premier database for systematic reviews on health care topics.
  • PubMed Clinical Queries provides a specialized search of PubMed to retrieve citations identified as systematic reviews, meta-analyses, reviews of clinical trials, evidence-based medicine, consensus development conferences, and guidelines. 
  • Embase: search for reviews on your topic in this database by selecting systematic review/Cochrane review/meta analysis from the EBM drop down list.
  • CINAHL (Cumulative Index to Nursing and Allied Health): search for reviews on your topic in this database by limiting to the publication type: systematic review.
  • Joanna Briggs Institute's JBI EBP Database includes systematic reviews, evidence summaries, and best practice information sheets.
  • Health Evidence is a free, searchable registry of quality-rated systematic reviews evaluating the effectiveness of public health interventions.
  • PROSPERO is an international database of prospectively registered systematic reviews in health and social care.
  • TRIP is a free search engine for systematic reviews, RCTs, and practice guidelines.
  • Center for Evidence-Based Dentistry, American Dental Association, has an evidence database that includes guidelines, critical summaries, and systematic reviews.
  • OTSeeker contains abstracts of systematic reviews, RCTs and other resources relevant to occupational therapy interventions.
  • PEDro is a free database of trials, systematic reviews, and practice guidelines in physiotherapy.
  • The Campbell Collaboration is an international research network that produces systematic reviews of the effects of social interventions in crime and justice, education, international development, and social welfare.
  • The Evidence for Policy and Practice Information and Co-ordinating Centre (EPPI-Centre) is part of the Social Science Research Unit at the Institute of Education, University of London. EPPI-Centre develops systematic reviews in social science and public policy. DoPHER (Database of Promoting Health Effectiveness Reviews), also by the EPPI-Centre, contains details of reviews of health promotion and public health effectiveness.
  • Healthy People 2020 Evidence-Based Resources includes systematic reviews relevant to Healthy People 2020 topics.
  • Systematic Review Data Repository (SRDR), from the AHRQ, is an open and searchable archive of systematic reviews and their data.
  • BEME: Best Evidence Medical and Health Professional Education lists published and in progress reviews in medical and health professional education.
  • COSMIN Database of Systematic Reviews of Outcome Measurement Instruments ; the COSMIN (COnsensus-based Standards for the selection of health Measurement INstruments) initiative aims to improve the selection of health measurement instruments.
  • PsycBITE indexes quality-rated systematic reviews, RCTs, and other studies on the cognitive, behavioral and other treatments for psychological problems occurring as a result of acquired brain impairment. 
  • SpeechBITE is a database of intervention studies related to speech pathology practice. It includes citations and abstracts from systematic reviews, RCTs, and other studies.
  • International Initiative for Impact Evaluation (3ie): Systematic Review Repository is a database of summaries of systematic reviews and protocols of the effectiveness of social and economic interventions in low and middle income countries. 
  • VetSRev is produced by the Centre for Evidence-based Veterinary Medicine and is a database of veterinary systematic reviews.
  • What Works Clearinghouse (WWC), Institute of Education Sciences, reviews the research on programs, products, practices and policies in education.

Timeline for a Systematic Review

Systematic reviews require a lot of time and effort to complete; a reasonable time frame is rarely under one year. The Cochrane Handbook for Systematic Reviews of Interventions, Box 2.3.b, suggests the following timeline to complete a Cochrane Review:             

Month Activity
1 - 2  Preparation of protocol
3 - 8   Searches for published & unpublished studies
2 - 3   Pilot test of eligibility criteria
3 - 8 Inclusion assessments
Pilot test of ‘Risk of bias’ assessment
3 - 10 Validity assessments
Pilot test of data collection
3 - 10 Data collection
3 - 10 Data entry
5 - 11 Follow up of missing information
8 - 10 Analysis
1 - 11 Preparation of review report
12 - Keeping the review up-to-date

Preparing for a Systematic Review: Things to Consider

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