Systematic reviews are sometimes mistakenly assumed to be 'literature reviews on steroids.' However, a systematic review differs greatly from a narrative (or literature) review. A systematic review is considered a primary study, whereas a narrative review is a secondary study. Systematic reviews also have distinct characteristics and goals. The two types of reviews are compared below in order to illustrate the differences between them:
|Review Element||Narrative Reviews||Systematic Reviews|
|Source of studies included||Not usually specified, potentially biased due to limited search approach||Comprehensive searches across specified databases, explicit search approach|
|Selection of studies||Not usually specified, potentially biased by reviewer||Selection performed using prespecified, universally applied inclusion and exclusion criteria|
|Evaluation||Variable levels of study evaluation||Rigorous critical evaluation using specified quality assessment instruments|
|Synthesis||Often Qualitative||Quantitative and/or qualitative. Some systematic reviews use statistical methods to synthesize quantitative data; these are meta-analyses|
|Inferences||Sometimes evidence-based but usually largely expert opinion backed with literature||Usually evidence-based, ideally with the majority of studies from more rigorously designed studies|
Table source: adapted [barely] from Cook K J. et. al. Ann Intern Med 1997: 126:376-380
The chart in the section titled 'Example of Literature Search' shows an example of a typical systematic review literature search, which involves
As noted below, completing a systematic review may take 3-12 months.
Differing from narrative reviews, a systematic review addresses a "...clearly formulated question that uses systematic and explicit methods to identify, select and critically appraise relevant research, and to collect and analyze data from the studies that are included in the review." (Cochrane Handbook) Because of this, the time commitment for a systematic review is significant, please plan ahead and be sure to leave enough time to work on your 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3 – 8 Searches for published and unpublished studies.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.
The PRISMA flow diagram (example shown below) is included in published systematic reviews to detail the workflow of a systematic review. Please note the number of initial articles retrieved for the systematic review; many systematic reviews may have considerably more articles captured during the initial search of electronic databases.
van den Berg, M. H., Schoones, J. W., & Vliet Vlieland, T. P. (2007). Internet-based physical activity interventions: A systematic review of the literature. Journal of Medical Internet Research, 9(3), e26. doi:10.2196/jmir.9.3.e26