Conducting comprehensive scoping reviews to systematically capture the landscape of a subject matter

Scientific publications or health research publications have seen a dramatic increase during the last few decades. Given this rapid production of information, literature reviews have become an imperative cornerstone for researchers to gain a better understanding of the research landscape that they are investigating. One type of literature review that has shown great utility is the scoping review, with its great efficiency in mapping existing literature and synthesizing knowledge. A step-by-step guide is provided in this article as an introduction to those who are interested in conducting scoping reviews in order to acquire a better picture of the research landscape. To help better understand the intricacies to conducting a scoping review, each step of the process is clearly explained and elaborated on. Each step is also followed by examples from published literature. The intended audience includes students and researchers new to scoping reviews. INTRODUCTION Scientific publications or health research publications have seen a dramatic increase during the last few decades. The US National Institute of Health reported that the number of publications indexed by MEDLINE at the National Library of Medicine was 712,675 in 2009 and this number increased to 956,390 in 2019. There was a 3.4% increase in publications indexed per year across the decade1. In this era of digitalization of information, the concept of grey literature as a body of information has surfaced in recent years due to the explosion of literature dissemination through nonconventional channels2. Grey literature databases are now also recognized as supplementary to academic databases2. To conduct research on a topic of interest, it is imperative to have a clear understanding of what has been done so far on the chosen topic. A comprehensive understanding of the work done so far reduces the possibility of duplication and helps researchers to plan and conduct research to advance our understanding of the topic. Thus, good homework is crucial before starting research on the chosen topic. A goal of good homework can be achieved by conducting a literature review. Generally, any well-done reviews would be undertaken through the phases shown in Figure 1. A literature review can range from a ‘simple narrative write-up’ to ‘comprehensive in-depth information extraction and summarization’. Nowadays more and more authors are conducting reviews for their research purpose. Some are doing them to gain an understanding of their research landscape, some are doing them to summarize what has been done so far, or some are coming up with pooled estimates to quantify the relationship between two variables. In this context, capturing the variability in objectives and related depth in methodology, several types of literature review have been used by the researchers3,4. A type of literature review that has shown great optimization and utility is the scoping review5,6. Scoping reviews are efficient at mapping existing literature on a given topic and synthesizing this knowledge. The nature of scoping reviews allows the researchers to capture the breadth of a research topic and are particularly useful in identifying the Methodology Paper | Population Medicine Popul. Med. 2021;3(December):36 https://doi.org/10.18332/popmed/143831 2 research landscape of a topic. Scoping reviews also provide a great utility in identifying research gaps in the literature and potential future steps in research. While this form of review is often used to identify the potential scope of a specific systematic review, it can also be used to summarize and disseminate information regarding research findings in the form of publications. Table 1 summarizes the differences between scoping and systematic reviews. METHODOLOGICAL APPROACH In this article, we will present in detail how to conduct a systematic scoping review based on common methodological frameworks5,7. These steps are described below with the example of a recently published review from our research group8. This review was conducted to summarize the research conducted on injury for Canadian immigrants8. Figure 2 outlines the steps for conducting a scoping review. Step 1: Narrowing down on a research question The first step in conducting a scoping review is to develop a research question based on the objectives and specific inquiries of the review. The purpose/objective of the scoping review is then used to guide the development of the inclusion and exclusion criteria. The principal idea or focus should be driven throughout the article to identify the breadth and depth of the scoping review. The PICOS framework can be used to define the breadth and depth of the research question9. PICOS is an acronym for: Population, Intervention, Comparison, Outcome, and Study design; and is often used for quantitative synthesis. Using these four parameters, a researcher can determine the breadth and depth of their research question. It is a fundamental part of the process as it can help to develop the research question and shape the focus of the scoping review. Alongside the PICOS framework, there are other frameworks that the researchers can use depending on the objective of the review. These include: Population, Intervention, Comparator(s), Outcomes, Context (PICOC); Condition, Context, Population (CoCoPop); Population, Index Test, Reference Test, Diagnosis of Interest (PIRD); Population, Exposure, Outcome (PEO); Population, Prognostic Factors, Outcomes (PFO); and Studies, Data, Methods, Outcomes (SDMO)10. An example of the PICOS framework is provided in Table 2. Step 2: Creating exclusion/inclusion criteria Having well-defined inclusion and exclusion criteria are crucial to the process of pursuing appropriate literature for a scoping review11. The inclusion and exclusion criteria are a reflection of the scope of the article and a guide that Figure 1. General steps of review Figur 1. G neral steps of review Table 1. Differences between scoping review and systematic review Scoping review Systematic review Summarizing the different types of research on a topic of interest Concentrating specific research evidence on a focused topic of interest Data charted according to selected key themes Defined protocol in extracting data (quantitative or qualitative) Broad capture of information Focused capture of information Identify and examine the methodology of research being studied Investigate and examine various results and conflicts Optional bias assessment Mandatory bias assessment Identify research gaps Present cumulative evidence Methodology Paper | Population Medicine Popul. Med. 2021;3(December):36 https://doi.org/10.18332/popmed/143831 3 determines the specificity or comprehensiveness of the review12. It acts as a guide for the reviewers to decide on what to include in the review and what to exclude. The reasoning and rationale behind each established criterion must be stated and justified clearly by the reviewers, so that there is no room for confusion to the reader. The languages and timeline considered for the inclusion criteria must be explicitly stated here by the reviewers (Table 3). Step 3: Formulating relevant keywords Formulating relevant keywords is a fundamental step required in the process of synthesizing a scoping review13. To determine relevant keywords, an initial limited search must be performed on the topic. This search then allows the researchers to screen the title and abstract of other articles and to identify relevant terms used by these articles. This initial limited search allows the researchers to further define their scope of the review and allows them to be more specific with their keywords so that the most relevant articles are found in the search14. This search also lets the researchers identify relevant search databases (Step 4) that need to be searched for this scoping review. This initial search allows to redefine the search strategy. Furthermore, search terms can be generally divided into two categories: Medical Subject Heading (MeSH), and keywords. MeSH terms are defined as terminology that is used by the National Library of Medicine database to catalogue and index health-related information15. These specific terms are used to index existing Table 2. Elaboration and explanation of PICOS with an example of a systematic review Elaboration of PICOS