"A systematic review attempts to collate all empirical evidence that fits pre-specified eligibility criteria in order to answer a specific research question. It uses explicit, systematic methods that are selected with a view to minimizing bias, thus providing more reliable findings from which conclusions can be drawn and decisions made (Antman 1992, Oxman 1993). The key characteristics of a systematic review are:
1. A clearly stated set of objectives with pre-defined eligibility criteria for studies;
2. An explicit, reproducible methodology;
3. A systematic search that attempts to identify all studies that would meet the eligibility criteria;
4. An assessment of the validity of the findings of the included studies, for example through the assessment of risk of bias; and
5. 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.cochrane.org.
A literature review is an assessment of a body of research that addresses a specific topic or research question. Also called a narrative review, this type of review has a wide scope and uses a non-standardized methodology. The search strategies, comprehensiveness, and time range covered will vary and do not follow an established protocol.
A scoping review often addresses a broader research question and can be used as preparation for a systematic review. The purpose of this type of review is to find all available information on a certain topic in order to identify gaps in the published and unpublished literature.
A mixed methods review is a systematic review that synthesizes two or more types of data (often quantitative and qualitative). This method of review is useful for multidisciplinary research questions or as a way to address the same overlapping or complementary review questions.
An umbrella review is, simply put, a review of systematic reviews written on a certain research topic. In order to maintain the highest level of research, only systematic reviews and meta-analyses are included in an umbrella review.