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) Note that different fields of research may use the terms differently: "In public health, the term 'systematic map' has been used to describe what in environmental sciences is referred to as a scoping review; a rapid review method for gaining a basic overview of the literature prior to defining full systematic reviews." [James, K.L., Randall, N.P. & Haddaway, N.R. A methodology for systematic mapping in environmental sciences. Environ Evid 5, 7 (2016). https://doi.org/10.1186/s13750-016-0059-6]
Evidence and Gap Maps (EGMs)
"EGMs are a systematic evidence synthesis product which display the available evidence relevant to a specific research question. The scope of a map is generally broader than that of a systematic review. We distinguish between EGMs which contain primary studies and reviews, mega-maps which include reviews and other maps, and maps of maps which contain only other maps. EGMs are used to identify gaps requiring filling with new evidence, collections of studies for review, and increase the discoverability and use of studies by decision-makers, research commissioners and researchers. They also highlight reviews which can be used to generate higher-level evidence products such as guidelines." (White et. al., 2020)
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)
