The following are the main types of reviews, but there are others as well.
Systematic Review
"Systematic reviews seek to collate evidence that fits pre-specified eligibility criteria in order to answer a specific research question. They aim to minimize bias by using explicit, systematic methods documented in advance with a protocol." (Cochrane Handbook, version 6.3, section 1)
Meta-Analysis
"Meta-analysis is the statistical combination of results from two or more separate studies. Potential advantages of meta-analyses include an improvement in precision, the ability to answer questions not posed by individual studies, and the opportunity to settle controversies arising from conflicting claims. However, they also have the potential to mislead seriously, particularly if specific study designs, within-study biases, variation across studies, and reporting biases are not carefully considered." (Cochrane Handbook, version 6.3, section 10)
Scoping Review (Systematic Map)
"Systematic Maps do not aim to answer a specific question, but instead collate, describe and map findings in terms of distribution and abundance of evidence, often configured in relation to different elements of a question." (CEE Guidelines and Standards for Evidence Synthesis in Environmental Management, version 5.0, section 2.4)
Evidence and Gap Maps (EGMs)
"EGMs are systematic and visual presentations of the availability of rigorous evidence for a particular policy domain. EGMs consolidate what we know and do not know about "what works" by mapping out existing and ongoing systematic reviews and impact evaluations in this field; and by providing a graphical display of areas with strong, weak or non-existent evidence on the effect of interventions or initiatives. A typical map is a matrix of intervention categories (rows) and outcome domain (columns). There may be additional filters for study design, location and population sub-group." (Campbell Collaboration)
Literature/Narrative Reviews
"The literature review method seeks to identify what has been accomplished previously, allowing for consolidation, for building on previous work, for summation, for avoiding duplication and for identifying omissions or gaps ... Literature reviews lack an explicit intent to maximize scope or analyse data collected. Any conclusions they may reach are therefore open to bias from the potential to omit, perhaps inadvertently, significant sections of the literature or by not questioning the validity of statements made." (Grant, M. J., & Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies. Health information & libraries journal, 26(2), 91-108. https://doi.org/10.1111/j.1471-1842.2009.00848.x)
