The following list of methodologies were identified in the literature in Grant and Booth (2009). These evidence synthesis models differ in the methodologies, scope, search strategy, amount of appraisal, approaches to synthesis, and types and levels of analysis. Methodologies are selected by researchers based on which methodology most closely maps to the research goals of the project. Librarians may be involved in support of any of these projects, but some methodologies require significantly greater librarian involvement than others.
A review that is seeking to boost a particular viewpoint on a topic or that is created to establish links to the existing literature without any statement regarding the comprehensiveness or scope of the search is frequently called a "literature review", "traditional review" or "interpretive review". It is characterized by a narrative format. It includes critiques of the literature but does not provide any information on how the literature was selected for inclusion. It is not reproducible. The authors cannot make claims about the completeness, rigor or replicability of their review.
Narrative reviews can be made more rigorous through the use of written, deliberately designed research questions and articulated keyword selection, such as the template that is included in Williamson et al.
Useful sources on this type of review include:
Critical review is very similar to a narrative literature review. It adds the component of critical appraisal, which separates it from the narrative review. It generally includes some analysis but the analysis is focused on seeking weaknesses in the body of the literature as a whole. The contribution of this methodology is to draw insight from the existing literature, and results in the development of research questions, hypotheses, or innovative models. The search focuses on finding items that are significant; however items are included based upon impact within the field rather than by assessed quality.
Mapping reviews take a step beyond critical reviews. The goals is to create a topical or concept map of the existing literature in order to define gaps in the literature. Mapping reviews are not comprehensive. They can be accomplished in a short period of time. There is no required quality assessment. The analysis is focused on the body of the literature, rather than the content of individual items. The goal is to identify the need for further research within the body of literature as a whole.
Meta-analysis is a methodology by which the results of quantitative research are combined in order to develop insight into the combined findings of the literature that has covered the same research question. Meta-analysis requires comprehensive search results in order to be able to make statements about the completeness and representation of the statistical analysis. Quality assessment is included, generally focused on inclusion and exclusion of studies that have similar methodologies. Most importantly, a statistician completes the final analysis using statistical analysis in order to identify the results of the meta-analysis.
Mixed methods reviews start from a research goal to identify both qualitative and quantitative research regarding a specified research question. This review type contrasts with meta-analysis, where the goal is to specifically identify the quantitative findings regarding a research question for the purpose of statistical analysis. Mixed methods reviews have a complex search process; it may require two separate searches that are targeted to quantitative research vs. qualitative research. There will still be systematized or systematic approaches to the development of the search, but the search is begun with the understanding that either the search designer must develop a very broad (sensitive) search or develop searches that are specifically tailored to the study methodologies being retrieved. There will be critical appraisal processes, but it may be that those processes need to be specifically tailored to the results of multiple search strategies and to quantitative vs. qualitative methodologies. Mixed methods reviews allow researchers to see the full breadth of findings and to look for gaps that have emerged within the quantitative and qualitative methodological methods.
A rapid review is used to determine the consensus on a policy or practice questions. It uses the same search methodologies as a systematic review, but it does not require a comprehensive search. It also usually constrained by the amount of time available to complete the search. It differs from a systematic review in the amount of literature included. It is similar in that it includes critical appraisal and identifies the quality of the literature on the topic.
Scoping reviews are performed with a goal to determine the potential size and scope of the available literature on a given research question. It aims to uncover not only published literature but also research on the topic that is currently underway. Scoping reviews may have time constraints similar to a rapid review. The main difference between a scoping review and a systematic review is that there is no critical appraisal step, because the goal isn't to establish the consensus, but just to identify the existence of the included items. A scoping review may include appraisal of the quantity and quality of the literature, but it doesn't synthesize conclusions.
State-of-the-art reviews are intended to identify current approaches and trends in the literature rather than a full retrospective. Inclusion criteria are date focused in addition to theme or research question. The goal is to comprehensively search on the specified research question while staying within a specified date scope. State-of-the art review does not require critical appraisal, not does it require any assessment of comprehensiveness. The analysis focuses on identifying the current trends and potential future innovations.
The systematized review uses techniques developed for systematic reviews but stops short of following the full systematic review process. The adoption of techniques developed for systematic reviews may be included depending upon the specific project that is designed. Search strings may or may not include comprehensive searching. It may or may not include assessment of quality of the included articles. The results disclose uncertainty and limitations of the methodology. It is clear in what decisions were made and why they were made in the methodology section. This may include having only one reviewer, not searching multiple databases, excluding important aspects of critical assessment, and setting scope limitations that decrease the level of comprehensiveness.
This was described in Grant and Booth (2009). There are no existing methodologies that have been published.
A research methodology with specific steps that aims to create a comprehensive, exhaustive search, appraise and synthesize the results and reveal findings on a broad swath of literature on a specific research methodology. These reviews have a number of techniques available to minimize bias in the results. It requires multiple participants to enhance inter-rater reliability. It also requires expert search string development. The goal is to articulate the quality of existing literature, any uncertainty that is in the findings, as well as projecting future hypotheses or gaps in the literature.
Umbrella review methodology allows an overarching review to aggregate findings from multiple systematic reviews. Umbrella reviews compare multiple interventions or potential solutions that could address one research hypothesis. This review type allows authors to determine if a narrow targeted approach to the hypothesis is preferable to a broader review and solution set. Umbrella reviews are most easily accomplished in disciplines with many systematic reviews in existence. The individual systematic reviews follow existing guidelines for the systematic review methodology, while the umbrella review is less specific or detailed and is looking at the general "intellectual conversation" being had across the resulting systematic reviews.