According to the Cochrane Library, "A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question. Researchers conducting systematic reviews use explicit methods aimed at minimizing bias, in order to produce more reliable findings that can be used to inform decision making. (See Section 1.2 in the Cochrane Handbook for Systematic Reviews of Interventions.)" About Cochrane
The key characteristics of a systematic review are:
(Chapter 1.2.2, 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 www.cochrane-handbook.org.)
What Are Systematic Reviews: a video from the Cochrane Consumers and Communication Group.
It takes time to develop exhaustive and comprehensive searches and additional time to review the results. Large citation retrievals (many thousand!) are possible depending on the topic.
Estimated timeline for completing a Cochrane systematic review:
1 – 2 Preparation of protocol.
3 – 8 Searches for published and unpublished studies.
2 – 3 Pilot test of eligibility criteria.
3 – 8 Inclusion assessments.
3 Pilot test of ‘Risk of bias’ assessment.
3 – 10 Validity assessments.
3 Pilot test of data collection.
3 – 10 Data collection.
3 – 10 Data entry.
5 – 11 Follow up of missing information.
8 – 10 Analysis.
1 – 11 Preparation of review report.
12 – Keeping the review up-to-date.
Source: 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 www.cochrane-handbook.org.