Systematic Reviews: Getting Started

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

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• Systematic and extensive searches to identify all the relevant published and unpublished literature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]

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. 

Source: Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. Browse the Handbook Online

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.