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Systematic Reviews: Introduction

The Glucksman Library's guide to assist researchers with completing systematic reviews.

What is a systematic review?

A systematic review is a high-level overview of primary research on a particular research question that tries to identify, select, synthesize and appraise all high quality research evidence relevant to that question in order to answer it.

– Definition from Cochrane Collaboration http://www.cochrane.org/about-us/evidence-based-health-care .

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Key components of systematic reviews

A clearly stated set of objectives with pre-defined eligibility criteria for studies;

  • Systematic and extensive searches to identify all the relevant published and unpublished literature
  • an explicit, reproducible methodology;
  • Study selection according to predefined eligibility criteria
  • Assessment of the risk of bias for included studies
  • Presentation of the findings in an independent and impartial manner
  • Discussion of the limitations of the evidence and of the review.

(Cochrane Handbook for Systematic Reviews of Interventions, 2011)

Why do we need systematic reviews?

The systematic review process has been developed to minimise bias and ensure transparency. Methods should be adequately documented so that they can be replicated. The systematic review is an approach used in health, education and social policy (as part of evidence based policy or practice) and is much more than a 'literature review' because it follows a strict methodology which means it is 'transparent, rigorous and replicable.'

When conducted well, systematic reviews should give us the best possible estimate of any true effect. An assessment of the methodological quality of reviews should highlight the limitations of a review.

Benefits include:

  • Save clinicians and researchers valuable time
  • Take a large mass of literature and make concise sense of it
  • Objectively evaluate the quality of evidence on a topic
  • Resolve or highlight contradictions in the literature
  • Guide clinical decisions
  • Form the basis for practice guidelines and health care policy
  • Identify the need for additional research
  • Prevent unnecessary studies from being carried out

Systematic reviews are gaining in popularity at medical research institutions across Europe and America. Guidelines either state the need for or highly recommend the involvement of a librarian or information professional when undergoing a systematic review project.  The Glucksman library and the Regional Medical library at ULH offer resources and library support for systematic review research.

Estimated timeline for completing a systematic review

Month                   Activity

1 – 2                   Preparation of protocol.

3 – 8                   Searches for published and unpublished studies.

2 – 3                   Pilot test of eligibility criteria.

3 – 8                   Inclusion assessments.

3                         Pilot test of ‘Risk of bias’ assessment.

3 – 10                 Validity assessments.

3                         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. 

Source: Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. Available from www.cochrane-handbook.org. Courtesy of the University of Maryland HS/HSL.

We would like to gratefully acknowledge the following for their contributions to this guide.

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Isabelle Delaunois
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Types of reviews

Narrative reviews: Broad perspective on topic (like a textbook chapter), no specified search strategy, significant bias issues, may not evaluate quality of evidence

Structured reviews: Includes a structured, but limited search, less bias, but not comprehensive, usually evaluates quality of evidence; a partial systematic review

Systematic reviews: Comprehensive with minimized bias, based on specific question and criteria with a pre-planned protocol, evaluates quality of evidence

  • Based on randomized controlled clinical trials (RCTs) – Best evidence
  • Based on other types of clinical studies or literature – Best available evidence
  • Meta-analysis – A quantitative systematic review that applies statistical analysis

Scoping Reviews: An overview of the literature on a broader topic; often done to identify whether a systematic review is feasible.