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Research: What is a systematic review?

What is a systematic review?

An effective systematic review "collates all empirical evidence that fits pre-specified eligibility criteria in order to answer a specific research question"  (Cochrane Handbook for Systematic Reviews of Interventions) .

The Centre for Reviews and Dissemination at York estimates that a  team will take 9-24 months to complete a systematic review. Systematic reviews can be of interventions (i.e. randomised controlled trials) or observations (i.e. case control or cohort studies).

A systematic review should have:

  • clearly stated objectives with pre-defined eligibility criteria for studies
  • explicit, reproducible methodology
  • a systematic search that attempts to identify all studies
  • assessment of the validity of the findings of the included studies (e.g. risk of bias)
  • systematic presentation, and synthesis, of the characteristics and findings of the included studies

“the quality of a systematic review depends on the quality of the studies appraised. It can be difficult to reach meaningful conclusions from reviews of low-level evidence, and thus, systematic reviews are commonly limited to high-level evidence (Level I or II) studies (RCTs)”.

Wright, R.W.,  Brand, R.A., Dunn,W. & Spindler, K.P. (2007). How to Write a Systematic Review. 

Why are systematic reviews necessary?

Problems with systematic reviews

Introduction to systematic reviews by Susan Shenkin)

Systematic Reviewlution is a living review of systematic reviews!  Here you will see evidence of where systematic reviews are not being done well.  Awareness of the problems will enable researchers to conduct better systematic reviews in future.

Systematic Review versus Literature Review




    Systematic Reviews          


  Literature Reviews


Focused on a single question (often PICO based)

Not necessarily focused on a single question - may describe an overview


A peer reviewed protocol or plan is included

No protocol included


Summarises the available literature

Summarises the available literature


Clear objectives are identified

Objectives may or may not be identified

Inclusion/Exclusion Criteria

Criteria stated before the review is conducted

Criteria not stated

Search Strategy

Comprehensive and systematic (stated in the document)

Strategy not explicitly stated (not always comprehensive or systematic)

Process of Selecting Articles

Usually clear and explicit

Not described in a literature review

Process of Evaluating Articles

Comprehensive evaluation of study quality

Evaluation of study quality may or may not be included

Process of Extracting Information

Usually clear and specific

Not clear or explicit

Results & Data Synthesis

Clear summaries of studies based on high quality evidence

Summary based on studies where the quality of the articles may not be specified. May also be influenced by the reviewer's theories, needs and beliefs.


Written by an expert or group of experts with a detailed and well grounded knowledge of the issues

Written by an expert or group of experts with a detailed and well grounded knowledge of the issues

(from Curtin University Library's Systematic Review guide)