A systematic review is a very rigorous type of evidence (or knowledge) synthesis that gathers, assesses and synthesizes all available empirical research on a specific question using a comprehensive search method, with a minimal amount of bias. Evidence synthesis refers to any method of identifying, selecting, and combining results from multiple studies (see Evidence Synthesis Review Types). Systematic reviews are a form of secondary analysis of data, because they use existing studies as their primary units of analysis.
Video source: The Cochrane Collaboration.
Important policy and practice decisions should not be made on the results of a single study. Replicability is an important principle of science and systematic reviews can tell us whether or how well results from one study are replicated in others.
According to the Cochrane organization: "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" (Cumpston et al., 2023). The Institute of Medicine* (2011) has stated that systematic reviews "systematically identify, select, assess, and synthesize the relevant body of research, and will help make clear what is known and not known about the potential benefits and harms of alternative drugs, devices, and other healthcare services.”
Systematic reviews are very important in nursing as they are one of the most reliable sources of evidence to guide clinical practice. The systematic review process is an efficient way to evaluate large amounts of information and the reviews are extremely useful for making healthcare decisions based on evidence from multiple studies. Well-conducted systematic reviews are generally considered to be a higher level of evidence for clinical decision-making than are individual studies (Best Practice, 2011). If conducted properly, systematic reviews and meta-analyses (a specialized subset of systematic reviews) are considered to be the highest levels of evidence on a given subject.
Systematic reviews are usually more comprehensive than traditional narrative literature reviews. The research question for a systematic review should be narrow in focus and the methodology should be transparent and reproducible. The systematic methodology attempts to minimize bias in the process.
Systematic reviews of randomized controlled trials (RCTs) using meta analysis to determine the effectiveness of a healthcare intervention are considered the highest level of evidence in medicine and allow a clinician to make the best and most up-to-date healthcare decisions on interventions or treatment (Remington & Toronto, 2020).
The literature search for a systematic review includes both published and unpublished literature (aka "grey literature"). Grey literature includes unpublished studies, reports, dissertations, conference papers and abstracts, governmental research, and ongoing clinical trials. Grey literature can be more current than published literature and there may be less publication bias.
Video source: The Incidental Economist - Healthcare Triage: Systematic Reviews, Aaron E. Carroll, MD, MS
References:
Cumpston M., Flemyng, E., Thomas, J., Higgins, J.P.T., Deeks, J.J., & Clarke, M.J. (2023). Chapter I: Introduction. In: J.P.T. Higgins, J. Thomas, J. Chandler, M. Cumpston, T. Li, M.J. Page, & V.A. Welch (Eds.). Cochrane handbook for systematic reviews of interventions (version 6.4.). Cochrane. www.training.cochrane.org/handbook.
*Note: IOM is now called the National Academy of Medicine