Systematic reviews

A literature review focused on a research question that tries to identify, appraise, select and synthesize all high quality research evidence relevant to that question

A review can be defined as, any attempt to synthesise the results and conclusions of two or more publications on any given topic.

Reviews are useful because of the sheer volume of biomedical literature that is now available. However, they have their limitations, a study by Mulrow of 50 reviews in the four of the major medical journals found that 49 had no statement of the methods used and 47 had inappropriate summaries of the information included.

Current medical reviews do not routinely use scientific methods to identify, assess and synthesise information.
C.D. Mulrow, 1987

These ‘traditional’ or narrative reviews have a number of biases. There is normally the personal bias of the author/s, a bias in the selection of included material, and with no clear methodology they cannot be reproduced independently, so assumptions cannot be easily verified.

In contrast a systematic review strives to comprehensively identify and track down all the available literature on a topic with clear comprehensive methodology described. The best examples of these are the Cochrane reviews.

The main stages in the systematic review process are :

  • Report all relevant primary studies
  • Assess methodological quality
  • Identify common definitions for outcomes
  • Extract estimates of outcomes
  • Meta-analysis where appropriate
  • Narrative summary where data sparse or of too low quality
  • Explore robustness of results
  • Clear presentation of key aspects
  • Appraisal of methodological limitations of primary studies and systematic review.

When a specific statistical strategy for combining the results of studies included in a systematic review is conducted this is termed a meta-analysis.  The key differences between narrative and systematic reviews are shown below.

Feature Narrative review Systematic Review
Question Broad Scope Focussed
Sources & Search Not usually specified Comprehensive & explicit
Appraisal Variable Rigorous
Synthesis Often qualitative summary Quantitative summary
Inferences Sometimes evidence-based Usually  evidence-based


  1. Mulrow CD. The medical review article: state of the science. Ann Intern Med. 1987;106:485-8. (click here for the abstract)



Journal Articles

Systematic reviews in health care from The British Medical Journa2001

( In order to access these BMJ articles you will need to register with the BMJ )

Meta-Analysis Series from The British Medical Journal 1997

( In order to access these BMJ articles you will need to register with the BMJ

Annals of Internal Medicine Articles 1997

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Other Resources