Methods for Research Evidence Synthesis: The Scoping Review Approach

Scoping reviews, like systematic reviews, require comprehensive and structured searches of the literature to maximize the capture of relevant information, provide reproducible results, and decrease potential bias from flawed implementations. The methodological framework for scoping reviews was developed by Arksey and O’Malley¹ and further refined by Levac et al.⁷ and the Joanna Briggs Institute.^6,8 Arksey and O’Malley’s framework for scoping reviews consists of the following six steps:

• Step 1: Identify the research question—the research question should be clearly defined and usually broad in scope to provide extensive coverage.
• Step 2: Identify relevant studies—the search strategy should be thorough and broad in scope and typically include electronic databases, reference lists, hand searches, and gray literature (ie, substantive or scholarly information that has not been formally published and often is not peer-reviewed), including conference abstracts, presentations, regulatory data, working papers, and patents.
• Step 3: Study selection—the study selection process can include post hoc, or modified, inclusion and exclusion criteria as new ideas emerge during the process of gathering and reviewing information.
• Step 4: Chart the data—the data extraction process in a scoping review is called data charting and involves the use of a data charting form to extract the relevant information from the reviewed literature.
• Step 5: Collate, summarize, and report the results—the description of the scope of the literature is commonly presented in tables and charts according to key themes.
• Optional Step 6: Consultation exercise—in this optional step, stakeholders outside the study review team are invited to provide their insights to inform and validate findings from the scoping review.

Since the number of studies included in a scoping review can be substantial, several study team members may participate in the review process. When multiple reviewers are employed, the team ought to conduct a calibration exercise at each step of the review process to ensure adequate interrater agreement. In addition, the PRISMA-ScR guidelines should be followed when reporting findings from scoping reviews to facilitate complete, transparent, and consistent reporting in the literature.⁴

The scoping review approach has several limitations. Scoping reviews do not formally evaluate the quality of evidence and often gather information from a wide range of study designs and methods. By design, the number of studies included in the review process can be sizable. Thus, a large study team is typically needed to screen the large number of studies and other sources for potential inclusion in the scoping review. Because scoping reviews provide a descriptive account of available information, this often leads to broad, less defined searches that require multiple structured strategies focused on alternative sets of themes. Hand searching the literature is therefore necessary to ensure the validity of this process. Scoping reviews do not provide a synthesized result or answer to a specific question, but rather provide an overview of the available literature. Even though statements regarding the quality of evidence and formal synthesis are avoided, the scoping review approach is not necessarily easier or faster than the systematic review approach. Scoping reviews require a substantial amount of time to complete due to the wide coverage of the search implicit in the approach.