How does a systematic review differ from a literature review?

Systematic reviews are NOT big literature reviews; systematic reviews are much more explicitly rigorous and systematic in their approach than literature reviews (Petticrew 2001). 

The table below (adapted from Bettany-Saltikov 2010a) explains the main differences:

  Systematic Review Literature Review
Question Focused on a single question Not necessarily focused on a single question but may describe an overview
Protocol A protocol or plan is included No protocol included
Background Provides a summary of the available literature on the topic Provides a summary of the available literature on the topic
Objectives Clear objectives are identified and stated Objectives may not be identified
Inclusion and exclusion criteria Criteria by which studies are included or excluded from the review are clearly stated at the outset. Criteria are not stated
Search strategy Comprehensive search is conducted in a systematic way (and described in the review) Strategy often not stated or described
Process of selecting articles Clearly stated in the review Often not stated
Process of evaluating articles Comprehensive evaluation of the quality of studies to be included in the review Quality is often not assessed or stated to be assessed
Extraction of relevant information Process of extracting relevant information is clearly described Process of extracting data is often not described
Results and data synthesis Clear summaries of studies based on high quality evidence, methods used should reduce likelihood of bias. Summary based on studies where quality may not have been assessed and possible bias less likely to have been addressed.

Challenging common myths and misconceptions

Petticrew (2001) dispels some of the other common myths about systematic reviews among them:

Myth - Systematic reviews include only randomised controlled trials and/or only quantitative evidence

While many reviews choose to include only RCTs (most, but not all, Cochrane Reviews concentrate on RCTs) this is not a requirement of a systematic review; many subjects lend themselves to a review of qualitative evidence.

Myth - Systematic reviews always involve statistical synthesis

They can include qualitative research and different forms of analysis.

Myth - Systematic reviews can only be used in medicine and health

As they provide "an efficient technique for hypothesis testing, for summarising the results of existing studies, and for assessing consistency among previous studies” (Petticrew 2001 p. 99) systematic reviews are not confined to health and medicine. Systematic reviews have been conducted in a variety of subjects including advertising, astronomy, biology, chemistry, criminology, ecology, education, law, manufacturing,  psychology, public policy, and zoology.

Myth - Systematic reviews are a substitute for doing good quality individual studies

Systematic reviews do not always find definitive answers on drugs, treatments etc.  They may conclude that more primary research is required.

Critical appraisal of systematic reviews

Not every publication which calls itself a systematic review is a true systematic review.

The AMSTAR (A MeaSurement Tool to Assess systematic Reviews) checklist allows you to logically appraise the quality of a systematic review. 

The PRISMA Statement (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) gives guidance on writing up and reporting systematic reviews. It can be helpful to use its checklist to compare a particular completed review against the standards set by PRISMA.

For general information on critical appraisal please see our library guide.