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