Systematic reviews are generally considered the most reliable source of evidence for decision making because they apply prespecified scientific methods to a synthesis of all the information on a given research question. Their value in decision making and guideline development is widely recognized by consumers, researchers, patients and clinicians.
A lot has changed since the first systematic reviews were published in the late 1970s. The rate of research output continues to accelerate and new and innovative ways of reviewing the evidence continue to emerge. These share the scientific approach of systematic review while addressing some limitations of the standard model, for example:
You might be wondering where meta-analysis fits into all of this. Often used interchangeably with systematic review, the term meta-analysis refers more correctly to a particular statistical technique that is sometimes used in a systematic review. Meta-analysis takes data from a group of studies and shows their estimated results together with a summary measure on a forest plot.
Elements of a Systematic Review:
Although systematic reviews may be the best known review type, there are a variety of different types of literature reviews that vary in terms of scope, comprehensiveness, time constraints, and types of studies included.
| Type of Review | Description | Time to Complete | Search Strategy |
|---|---|---|---|
| Narrative/Literature Review | Narrative literature review collates relevant studies and drawn conclusions from them. A narrative review, often referred to as a traditional literature review, resembles a storytelling journey through existing research. It intertwines key findings, trends, and theories related to a topic without the strict structure characteristic of systematic reviews. Instead of analyzing data, it provides a broader perspective, emphasizing what is known, what is absent, and the current discussions in the field. Excellent choice if working solo. | 2+ months |
Not comprehensive which could introduce bias.
Javeed Sukhera; Narrative Reviews in Medical Education: Key Steps for Researchers. J Grad Med Educ 1 August 2022; 14 (4): 418–419. doi: https://doi.org/10.4300/JGME-D-22-00481.1 |
| Scoping Review |
Researchers use scoping reviews to map the depth and breadth of emerging areas in a specific area, allowing them to include different forms of literature and thus not be limited to peer-reviewed literature. Scoping review teams must use a systematic and rigorous approach to produce a synthesis of the common concepts identified in the diverse existing literature. Preliminary assessment of potential size and scope of available research literature. Aims to identify nature and extent of research evidence. (usually ongoing research). A scoping review might be used to map evidence and key concepts in fields that are new or very broad in scope, or where there is not enough data to make an effective synthesis. They may sometimes be done as a preliminary step to a systematic review. |
2+ months |
Completeness of searching determined by time/scope constraints. Librarian collaboration recommended. Scoping reviews are not conducted by a single individual - a team is needed.
Susanne Mak, Aliki Thomas; An Introduction to Scoping Reviews. J Grad Med Educ 1 October 2022; 14 (5): 561–564. doi: https://doi.org/10.4300/JGME-D-22-00620.1 Susanne Mak, Aliki Thomas; Steps for Conducting a Scoping Review. J Grad Med Educ 1 October 2022; 14 (5): 565–567. doi: https://doi.org/10.4300/JGME-D-22-00621.1 |
| Rapid Review | Assessment of what is already know about a policy or practice issue, by using systematic review methods to search and critically appraise existing research. A rapid review provides a rapid synthesis of knowledge about a policy or clinical practice issue and attempts to inform an evidence-based decision quickly. It follows many of the stages of a systematic knowledge synthesis but may modify stages to shorten the timeline. | 2-6 months | Completeness of searching determines time constraints. librarian collaboration recommended. |
| Integrative Review | An integrative review is a specific review method that summarizes past empirical or theoretical literature to provide a more comprehensive understanding of a particular phenomenon or healthcare problem. Well-done integrative reviews present the state of the science, contribute to theory development, and have direct applicability to practice and policy. Reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives are generated. | 2-10+ months | Aims for exhaustive, comprehensive search. Librarian collaboration recommended |
| Umbrella Review | Review other systematic reviews and meta-analyses on a topic. Focuses on broad conditions or problems for which there are competing interventions and highlights reviews that address these interventions. | 2+ months | Identification of component reviews but no primary studies. Librarian collaboration recommended |
| Systematic Review |
Systematic reviews are research reviews that combine the evidence of multiple studies regarding a specific clinical problem to inform clinical practice and are the method of choice for evidence-based practice initiatives (that is, Cochrane Collaboration). Systematic reviews require a well-specified clinical question, explicit methods, and a comprehensive search for relevant primary studies. Systematic reviews often include the statistical methods of meta-analysis if primary studies meet the assumptions required for meta-analyses. If primary studies cannot be combined statistically, a narrative analysis is undertaken in conjunction with vote counting or other quasi-statistical approaches. Attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question; using explicit methods aimed at minimizing bias, in order to produce more reliable finding that can be used in decision making. |
10-12+ months |
Aims for exhaustive, comprehensive search. Librarian will develop search strategy and write methodology section of the manuscript Need to assemble a team to work on this project |
| Meta-Analysis |
Meta-analysis is a research review method that combines the evidence of multiple primary studies by employing statistical methods, thus enhancing the objectivity and validity of findings. The research design and hypotheses of primary studies need to be very similar, if not identical. With the meta-analysis approach, each primary study is abstracted, coded, and entered into a quantitative database. Findings are subsequently transformed into a common metric to calculate an overall effect size. A significant advantage of the meta-analysis method is that adjustment for sample size and study quality can be included in the analysis. Technique that statistically combines the results of quantitative data to provide a more precise effect of the results. The term meta-analysis refers more correctly to a particular statistical technique that is sometimes used in a systematic review. Meta-analysis takes data from a group of studies and shows their estimated results together with a summary measure on a forest plot. Any of the review types discussed above could include one or more meta-analysis. |
10-12+ months | Statistical technique for combining finding from disparate quantitative studies. Librarian will develop search strategy and write methodology section of the manuscript. |
