All searching should be conducted thoroughly. However, some research questions do not require systematic review methodology. Some research questions are better suited to different review methodologies based on the realistic landscape of how much and what quality of literature is published on a topic at a given time. Additionally, some researchers may have limited time requirements that makes the planning and conduction of a systematic review impractical. In these instances, researchers may want to consider alternatives such as rapid reviews or systematized literature reviews.
Before beginning any review type, researchers should do sufficient preliminary searching to determine what review type is suitable for the research topic/question.
There are other types of reviews, and some are often mistaken for systematic reviews. Some may even call themselves 'systematic reviews.' However, understanding the scope of other reviews and methods can help one distinguish between them and a systematic review proper. Here are some common review types:
The above definitions are taken from A typology of reviews: an analysis of 14 review types and associated methodologies.The document is listed below.
Meta-analysis is the use of statistical methods to summarise the results of independent studies. By combining information from all relevant studies, meta-analyses can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review. Meta-analyses also facilitate investigations of the consistency of evidence across studies, and the exploration of differences across studies (Cochrane Handbook, 1.2.2). More information on meta-analyses can be found in Cochrane Handbook, Chapter 9.
A meta-analysis goes beyond critique and integration and conducts secondary statistical analyses on the outcomes of similar studies. Systematic reviews may use quantitative methods to synthesize and summarize the results.
An advantage of a meta-analysis is the ability to be completely objective in evaluating research findings. Not all topics, however, have sufficient research evidence to allow a meta-analysis to be conducted. In that case, an integrative review is an appropriate strategy.
Literatures reviews focus on the existing literature of a subject. They lack the rigorous systematic methodology of systematic reviews. They rarely conduct exhaustive search strategies and do not publish the search strategy (although there are exceptions due to the general nature of literature reviews.) Literature reviews may examine the literature that is the most commonly cited within a certain time frame. Synthesis according to some criteria is typically employed. Literature reviews can take many forms: theses, dissertations, a component within a research paper, or lab report. Please see the University of North Carolina at Chapel Hill's information on literature reviews here.
In general, scoping reviews are commonly used for ‘reconnaissance’ – to clarify working definitions and conceptual boundaries of a topic or field. Scoping reviews are useful for when a body of literature has not yet been comprehensively reviewed, or exhibits a complex or heterogeneous nature not amenable to a more precise systematic review of the evidence. While scoping reviews may be conducted to determine the value and probable scope of a full systematic review, they may also be undertaken as exercises in and of themselves to summarize and disseminate research findings, to identify research gaps, and to make recommendations for future research.
From Peters, MD, Godfrey, CM, Khalil, H, McInerney, P, Parker, D & Soares, CB 2015, 'Guidance for conducting systematic scoping reviews', International Journal of Evidence-Based Healthcare, vol. 13, no. 3, pp. 141-146:
Rapid reviews utilize systematic review methodology, but they have a more streamlined process for possible time constraints. Defining the limitations and the drawbacks of implementing a streamlined process (and a process that may not incorporate all the components of a systematic review for transparency and systematization) must be described. To learn more about rapid reviews, check out the link below.
An Umbrella review is a synthesis of existing reviews, only including the highest level of evidence such as systematic reviews and meta-analyes. It specifically refers to a review that compiles evidence from multiple reviews into one accessible and usable document. Umbrella reviews focus on either a broad condition or problem for which there are competing interventions. These reviews can highlight the different interventions and their results.
Methodology paper: Aromataris, E, Fernandez, R, Godfrey, CM, Holly, C, Khalil, H & Tungpunkom, P 2015, 'Summarizing systematic reviews: Methodological development, conduct and reporting of an umbrella review approach', Int J Evid Based Healthc, vol. 13, no. 3, pp. 132-140.
A systematized review attempts to include elements of the systematic review process while stopping short of the systematic review. Systematized reviews are typically conducted as a postgraduate student assignment, in recognition that they are not able to draw upon the resources required for a full systematic review (such as having two reviewers for extensive literature screening).