Systematic reviews

"Systematic reviews aim to identify, evaluate and summarise the findings of all relevant individual studies, thereby making the available evidence more accessible to decisionmakers. When appropriate, combining the results of several studies gives a more reliable and precise estimate of an intervention’s effectiveness than one study alone." 

Centre for Reviews and Dissemination 2009, Systematic Reviews: CRD's guidance for undertaking reviews in health care, Centre for Reviews and Dissemination, York.

 
"The key characteristics of a systematic review are:

• a clearly stated set of objectives with pre-defined eligibility criteria for studies;
• an explicit, reproducible methodology;
• a systematic search that attempts to identify all studies that would meet the eligibility criteria;
• an assessment of the validity of the findings of the included studies, for example through the assessment of risk of bias; and
• a systematic presentation, and synthesis, of the characteristics and findings of the included studies."

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 http://handbook-5-1.cochrane.org/ 

Systematic reviews are very different to narrative reviews. The list below highlights some of the principle features which set systematic and narrative reviews apart.

Systematic Review

• Has a clear question or hypothesis to be answered
• Searches are rigorous to locate all potentially relevant literature
• Includes explicit inclusion exclusion criteria
• Assesses study quality for inclusion and provides a synthesis of results

Narrative (Traditional) Review

• Starts with a question but includes general discussion and no hypothesis
• Does not locate all relevant literature
• Does not have explicit inclusion / exclusion criteria
• Does not always require included studies to be methodologically sound or of a certain quality

Mark, P. (2001). "Systematic reviews from astronomy to zoology: myths and misconceptions." BMJ 322(7278): 98-101