---
title: "Systematic review"
chunk: 2/6
source: "https://en.wikipedia.org/wiki/Systematic_review"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:26:30.659047+00:00"
instance: "kb-cron"
---

=== Scoping reviews ===
Scoping reviews are distinct from systematic reviews in several ways. A scoping review is an attempt to search for concepts by mapping the language and data which surrounds those concepts and adjusting the search method iteratively to synthesize evidence and assess the scope of an area of inquiry. This can mean that the concept search and method (including data extraction, organisation and analysis) are refined throughout the process, sometimes requiring deviations from any protocol or original research plan. A scoping review may often be a preliminary stage before a systematic review, which 'scopes' out an area of inquiry and maps the language and key concepts to determine if a systematic review is possible or appropriate, or to lay the groundwork for a full systematic review. The goal can be to assess how much data or evidence is available regarding a certain area of interest. This process is further complicated if it is mapping concepts across multiple languages or cultures.
As a scoping review should be systematically conducted and reported (with a transparent and repeatable method), some academic publishers categorize them as a kind of 'systematic review', which may cause confusion. Scoping reviews are helpful when it is not possible to carry out a systematic synthesis of research findings, for example, when there are no published clinical trials in the area of inquiry. Scoping reviews are helpful when determining if it is possible or appropriate to carry out a systematic review, and are a useful method when an area of inquiry is very broad, for example, exploring how the public are involved in all stages systematic reviews.
There is still a lack of clarity when defining the exact method of a scoping review as it is both an iterative process and is still relatively new. There have been several attempts to improve the standardisation of the method, for example via a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline extension for scoping reviews (PRISMA-ScR). PROSPERO (the International Prospective Register of Systematic Reviews) does not permit the submission of protocols of scoping reviews, although some journals will publish protocols for scoping reviews.

== Stages ==
While there are multiple kinds of systematic review methods, the main stages of a review can be summarised as follows:

=== Defining the research question ===
Some reported that the 'best practices' involve 'defining an answerable question' and publishing the protocol of the review before initiating it to reduce the risk of unplanned research duplication and to enable transparency and consistency between methodology and protocol. Clinical reviews of quantitative data are often structured using the mnemonic PICO, which stands for 'Population or Problem', 'Intervention or Exposure', 'Comparison', and 'Outcome', with other variations existing for other kinds of research. For qualitative reviews, PICo is 'Population or Problem', 'Interest', and 'Context'.

=== Searching for sources ===
Relevant criteria can include selecting research that is of good quality and answers the defined question. The search strategy should be designed to retrieve literature that matches the protocol's specified inclusion and exclusion criteria. The methodology section of a systematic review should list all of the databases and citation indices that were searched. The titles and abstracts of identified articles can be checked against predetermined criteria for eligibility and relevance. Each included study may be assigned an objective assessment of methodological quality, preferably by using methods conforming to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, or the standards of Cochrane.
Common information sources used in searches include scholarly databases of peer-reviewed articles such as MEDLINE, Web of Science, Embase, and PubMed, as well as sources of unpublished literature such as clinical trial registries and grey literature collections. Key references can also be yielded through additional methods such as citation searching, reference list checking (related to a search method called 'pearl growing'), manually searching information sources not indexed in the major electronic databases (sometimes called 'hand-searching'), and directly contacting experts in the field.
To be systematic, searchers must use a combination of search skills and tools such as database subject headings, keyword searching, Boolean operators, and proximity searching while attempting to balance sensitivity (systematicity) and precision (accuracy). Inviting and involving an experienced information professional or librarian can improve the quality of systematic review search strategies and reporting.

=== 'Extraction' of relevant data ===

Relevant data are 'extracted' from the data sources according to the review method. The data extraction method is specific to the kind of data, and data extracted on 'outcomes' is only relevant to certain types of reviews. For example, a systematic review of clinical trials might extract data about how the research was done (often called the method or 'intervention'), who participated in the research (including how many people), how it was paid for (for example, funding sources) and what happened (the outcomes). Relevant data are being extracted and 'combined' in an intervention effect review, where a meta-analysis is possible.

=== Assess the eligibility of the data ===
This stage involves assessing the eligibility of data for inclusion in the review by judging it against criteria identified at the first stage. This can include assessing if a data source meets the eligibility criteria and recording why decisions about inclusion or exclusion in the review were made. Software programmes can be used to support the selection process, including text mining tools and machine learning, which can automate aspects of the process. The 'Systematic Review Toolbox' is a community-driven, web-based catalog of tools, to help reviewers chose appropriate tools for reviews.