How to write a scoping review? – A comprehensive guide

Abstract

Systematic reviews occupy a higher order of hierarchy in the evidence pyramid; however, certain questions are left unanswered since a quantitative synthesis is difficult to achieve when there is limited and heterogeneous data. The scoping reviews thereby play a pivotal role in covering the gap in knowledge acting as a precursor to systematic reviews. They also aid in giving guidance for the scope of future research and the parameters that must be considered in future studies. To the best of our knowledge, limited scoping reviews have been conducted so far which could be attributed to a lack of awareness on what is the aim of scoping reviews and how does it contribute to evidence-based medicine. As a result, the purpose of this article is to highlight how a scoping review should be conducted.

INTRODUCTION

Evidence-based medicine has gained utmost importance over the past few decades. It is the combination of the best available and current research evidence with clinical experience and patient needs. When comparing the hierarchy in evidence-based medicine, systematic reviews occupy a higher order following the scoping reviews. The scoping reviews are different from the other kind of reviews in the respect that it serves as a precursor for systematic reviews.^[1] We aim to define the difference between both these terms and provide data on how to frame a scoping review. We aim to highlight the difference between the two and also throw light on the structure of a scoping review.

In 2009, Grant and Booth characterized the reviews into 14 different types.^[2] Scoping reviews, also referred to as “scoping studies” are one type of review.^[3,4] They can be characterized as exploratory projects that methodically map the available literature on a certain topic. “Scoping Studies” can also recognize sources of evidence, key concepts, and any gaps in the literature.^[5]

The original framework for conducting such reviews was proposed by Arksey and O’Malley, in 2005.^[6] Levac et al. later advanced and extended this framework in 2010.^[7] Further refinement was incorporated in the scoping review methodology and corresponding guidance was then refined by a working group from Joanna Briggs Institute (JBI) and the JBI collaboration in 2015.^[8]

The Preferred Reporting Items for Systematic Reviews (PRISMA) statement was expanded to include scoping reviews in the year 2018.^[9]

SCOPE OF SCOPING REVIEW

Scoping reviews are designed to “map” the existing evidence and can be considered to be a precursor to systematic reviews.^[3]

Exploring the breadth of literature, mapping and summarizing the evidence, and providing recommendations for future research are the three most essential reasons for performing a scoping review.^[10]

The above-mentioned reasons help to measure the extent, range, and nature of the evidence in question. They also assist in summarizing the findings which are heterogeneous in methods or discipline, from a body of knowledge. These reasons also aid in identifying gaps in the literature to further assist in planning future research.^[9,11]

Limited scoping reviews have been conducted so far. The idea behind conducting a scoping review is to look for the gap in the literature body and hence provide a pathway to conduct more relevant clinical studies with definite inclusion–exclusion criteria. This ultimately helps clinicians and researchers to accurately answer a research question, thereby helping in clinical decision-making. Scoping reviews pave a guiding path toward future directions in evidence-based medicine by functioning as a precursor to systematic reviews.

DIFFERENCE BETWEEN A SYSTEMATIC REVIEW AND SCOPING REVIEW

A systematic review typically compiles evidence from quantitative literature to answer questions regarding the effectiveness of a given solution for a specific condition. A scoping review, on the other hand, provides a broader perspective which aids in clarifying working definitions and conceptual boundaries of a topic, thereby filling the gaps in existing knowledge. The inclusion and exclusion criteria typically for a scoping review can be developed posthoc, whereas for systematic reviews, it is defined at outset. The methodological quality plays a crucial role in the synthesis of systematic reviews; however, for scoping reviews, all data are included, including the gray literature irrespective of its methodological quality. It, therefore, becomes integral that a scoping review develops apriori protocol which must also be included in the review. The protocol should ideally be registered to ensure transparency and reduce duplication of work. Unlike systematic reviews, having the PICO framework, which includes participants/population (includes characteristics of participants), intervention (treatment of interest), comparator (control group), outcome (the main effect of treatment expected), and the framework for scoping reviews concentrate on population, concept, and context (PCC). The population includes the important characteristics of the participants such as age criteria and gender). The concept implies the core idea of the review, interventions, phenomenon of interest, and outcomes. The context in the framework includes cultural factors, racial factors, geographical or location factors, and gender-based health-care settings.^[11,12]

For example, in a systematic review conducted by Gupta etal., titled – Anesthetic efficacy of primary and supplemental buccal/lingual infiltration in patients with irreversible pulpitis in human mandibular molars: a systematic review and meta-analysis, the PICO framework includes population: human mandibular teeth with irreversible pulpits, intervention: anesthesia with Inferior Alveolar Nerve Block (IANB), comparison: anesthesia with IANB + supplementary intraligamentary injection, and outcome: successful anesthesia and painless root canal treatment procedure.^[13]

Another example for a systematic review titled – Diabetes mellitus and the healing of periapical lesions in root-filled teeth: a systematic review and meta-analysis of the PICO framework includes: population: root canal treated teeth, intervention: diabetics, comparison: nondiabetics, and outcome: healing outcome in presence or absence of radiolucent periapical lesions.^[14]

Virdee etal. titled – Efficacy of irrigant activation techniques in removing intracanal smear layer and debris from mature permanent teeth: a systematic review and meta-analysis, the PICO framework includes: population – mature permanent teeth, intervention – activation technique, comparison – conventional techniques, and outcome – smear layer removal.^[15] For a scoping review, titled – Influence of vehicle for calcium hydroxide on postoperative pain: a scoping review, the PCC framework includes: population – endodontically treated teeth receiving calcium hydroxide medicament, concept – influence of the vehicle on postoperative pain, and context – calcium hydroxide.^[16] In another study entitled – Effect of root canal irrigants on the mechanical properties of endodontically treated teeth: A scoping review, the PCC framework includes: population – endodontically treated teeth, concept – influence of irrigants on mechanical properties of teeth, and context – dentistry.^[17]

Scoping reviews, having a broader perspective, have both qualitative and quantitative synthesis in comparison to systematic reviews. Scoping reviews do not necessitate the use of any critical appraisal tools and the application of risk of bias assessment. Hence, the use of statistical meta-analysis (for prevalence, incidence, effectiveness, diagnostic accuracy, risk or etiology, and psychometric or prognostic data) or meta-synthesis (expert or experiential opinion data) or both is typically not administered in a scoping review.

THE PREFERRED REPORTING ITEMS FOR SYSTEMATIC REVIEWS EXTENSION FOR SCOPING REVIEWS

The PRISMA extension for Scoping Reviews (PRISMA-ScR) was established in accordance with the guidance published by the Enhancing the QUAlity and Transparency Of health Research Network for the development of reporting guidelines.^[18]

The PRISMA-ScR is a standard for reporting scoping reviews that was developed by PRISMA. The original PRISMA statement was adapted adjustments were made to generate this PRISMA extension: five things were eliminated (since they were considered unrelated to scoping reviews) and two items were rendered optional. The items eliminated in the methodology section included – item 13 (summary measures), item 15 (risk of bias across studies), and item 16 (additional analyses). Two items were eliminated from the results section – item 22 (risk of bias across the studies) and item 23 (any additional analyses). Item 12 and 19 were rendered optional which includes critical appraisal in both the methods and results section.^[9]

These guidelines are in keeping with the JBI scoping review guidance, which emphasizes the need for methodological rigor in these reviews. The PRISMA-ScR is expected to improve scoping review reporting and surge their relevance for decision-making, as well as that future adherence to reporting standards, be examined, which will be crucial in determining its impact.

The PRISMA extension checklist is can be described under the following sections:

• Item 1 (Title) – The title is the topic or the research question to be studied under the scoping review. For example, in the article entitled – Influence of vehicle for calcium hydroxide on postoperative pain: A scoping review, the title represents the research question – does the vehicle for calcium hydroxide influence the postoperative pain levels in patients undergoing nonsurgical endodontic treatment?
• Item 2 (Abstract) – This section includes a structured summary including background, objectives, eligibility criteria, and search databases such as PubMed, and Scopus. Data charting methods used such as tabular form, graphic form, and word clouds result and conclusion with reference to the research question
• Introduction – This section is broadly divided into two items; item 3 – rationale and item 4 – objectives. It consists firstly of the background of the research topic, the lacunae, need for the research topic with an explanation of PCC criteria, which is explained ahead
• Methods – This section includes 12 items, out of which three are omitted as explained earlier. Item 5 highlights the review protocol and the registration information. Apriori protocol is essential to be developed and the details of which must be mentioned therein^[1,8]
• Item 6 includes the eligibility criteria that need to be defined in terms of language considered, publication status, and whether or not gray literature is included
• Item 7 includes information sources, for example, the databases searched with the dates covered
• Item 8 represents the search strategy, for example, in the article entitled – Influence of vehicle for calcium hydroxide on postoperative pain: A scoping review, the search strategy based on the research question included ([Calcium Hydroxide] OR [Intra Canal Medicament] OR [Intra Canal Medication] OR [Medicament] OR Vehicle OR Saline OR Peg] AND ([Postoperative Pain] OR [Inter Appointment Pain] OR [Flare Up] OR [Endodontic Flare Ups] OR [Endodontic Pain])^[16]
• Item 9 includes the screening and eligibility criteria, whether the process was iterative or standardized, and how many reviewers screened the data
• Item 10 includes the data charting process. The process of data charting, whether tabular, graphic, or any other tool is used. For example in the article entitled – Influence of vehicle for calcium hydroxide on postoperative pain – A scoping review,^[16] data charting was done in a tabular form under the following headings – the title of the article journal along with the author, country where the study was conducted, study type, inclusion criteria, intervention group, and intervention time and placement method
• Item 11 includes data items wherein any variables in the data charting process, if considered must be mentioned
• Item 12, which includes critical appraisal of individual sources of evidence is rendered optional in case scoping review
• Item 13 includes summary measures which are not required in scoping review since meta-analyses are not performed in such reviews due to heterogeneity
• Item 14 includes a synthesis of results which can again be charted in a tabular form, for example, in the article entitled – Influence of vehicle for calcium hydroxide on postoperative pain: A scoping review, the results were tabulated under the following headings – study, the outcome assessed, the tool for assessing the outcome, time period, and the result
• Items 15 and 16 are excluded from scoping reviews which include the risk of bias and additional analyses.
• Results – This section further includes seven items. Pertaining to the methods, these items must be included in the results section (Item 17 – selection of sources of evidence, item 18 – characteristic of evidence, item 19 – critical appraisal within the sources of evidence, which is rendered optional, item 20 – the result of individual sources of evidence, item 21 – synthesis of result; just like the methods section, items 22 and 23 are eliminated from scoping review criteria which include risk of bias and additional analyses^[9]
• The discussion section must include the following: item 24 (summary of evidence), which provides an overview of the evidence available pertaining to the objectives of the study
• Item 25 discusses the limitation of the studies conducted to identify lacunae in the literature to pave the way for future research. Item 26 includes the conclusion section which must highlight the potential for future research
• Item 27 highlights the funding. The authors need to outline the nature and source of funding for the collection of data for conducting the scoping review.^[9]

FRAMEWORK OF SCOPING REVIEW

The framework which was originally brought forward by Arksey and O’Malley in 2005 has been noteworthy in how scoping reviews are conducted. Further work by Levac et al. (2010) has supplemented this framework.^[7] Both these frameworks have reinforced the approach by JBI to conduct scoping reviews. The framework provided by Arksey and O’Malley and Levac et al. consisted of six parameters, however, the approach developed by JBI consisted of nine parameters building the backbone for the synthesis of a scoping review.^[19]

The framework, as proposed by Peters etal. includes the following parameters,

1. Define and align the question/s and objective/s
2. Define and align inclusion criteria with the objective/s
3. Mark out the planned approach to search for evidence, select, extract data, and present the evidence
4. Exploration
5. Evidence selection
6. Extraction
7. Evidence analysis
8. Presentation of the findings
9. Summarizing the evidence, making conclusions, and noting any implications of the findings.

DEVELOPMENT AND REGISTRATION OF SUITABLE PROTOCOL

Before beginning the scoping review, an apriori protocol must be devised, similar to a systematic review. This protocol is significant because it predefines the review’s objectives, methodology, and reporting, ensuring that the process is transparent. The protocol lays out the study’s strategy and aids in the avoidance of reporting bias if any. The protocol and reporting of a scoping review must be congruent with the PRISMA-Scr.

Just like the systematic review, the scoping review must be registered in one of the databases. PROSPERO is currently ineligible for registering scoping reviews; however, registration can be done in Open Science Framework or Figshare. In addition, they can even be published in certain journals like “JBI Evidence Synthesis.”^[12]

TITLE AND INTRODUCTION

The PCC’s essential elements must be reflected in the protocol’s title. A scoping review generally has one primary question, for example, when an observer wants to realize the impact of irrigants on the mechanical properties of teeth treated endodontically, the core elements of the PCC, namely, endodontically treated teeth (population), the effect of irrigants on mechanical properties (concept), and endodontics (context) are highlighted in the title – Effect of root canal irrigants on the mechanical properties of endodontically treated teeth: A scoping review.^[8]

The introduction should be thorough, covering all the major aspects of the subject under consideration. The aim of the review must be clearly stated. This section work should clearly define the topic of interest.

INCLUSION CRITERIA AND TYPE OF EVIDENCE

The term “inclusion criteria” refers to the criteria used to determine which research will be considered for inclusion in the review. Justification and rationale for including the said criteria should be thoroughly explained in the background. The search strategy must be comprehensive for the identification of both unpublished and published literature. There is no limitation in including the type of study. All studies relevant to the inclusion criteria including any existing literature such as preliminary research studies, in vitro studies, systematic reviews, meta-analyses, letters, guidelines, and websites must be taken into consideration. Including studies without any language, the restriction is recommended, however, if restricted, a detailed explanation must be given.

The pertinent attributes of the participants must be detailed, such as sex, and age which will match the review question and are appropriate for the objectives of the study.

The inclusion criteria must be in accordance with the PCC criteria. As in our exemplar study titled – Effect of root canal irrigants on the mechanical properties of endodontically treated teeth: A scoping review, the population included teeth of both human and animal origin. The concept focuses on the effect of irrigants on the mechanical properties of endodontically treated teeth and context-general dentistry.^[17]

In another review by Riberio etal., the inclusion criteria addressed clinical, in vitro, invivo, and in situ studies (population), evaluating antimicrobial alternatives to triple antibiotic paste (concept) in regenerative endodontics (context).^[20]

SEARCH STRATEGY

As previously indicated, the search method should aim to be as comprehensive as possible, encompassing both published and unpublished gray literature. The search can be carried out in both standardized and iterative forms, wherein the charting table is continuously updated.

A three-step search strategy must be utilized as recommended by JBI. The first step focuses on an initial search that is limited to at least two appropriate online databases such as PubMed/MEDLINE and CINAHL. This preliminary search is followed by an analysis of the titles and abstracts of retrieved papers, which is followed by a thorough analysis of the reference lists of the sources selected from the full-text analysis.^[21]

DATA EXTRACTION AND CHARTING

The approach used for data extraction in a scoping review is referred to as “Data Charting,” and it gives the reader a rational and descriptive overview of the findings that fit with the scoping review’s objectives and queries.

Items to extract must include a citation, aims, the country where the study was conducted, population and sample size, methods, intervention type, comparison group, duration of intervention, outcomes, and details.

ANALYSIS OF EVIDENCE

It is noteworthy that scoping reviews do not quantitatively synthesize the results or outcomes of the studies included, as it is done in systematic reviews. In a scoping review, qualitative content analysis is descriptive, and synthesizing the data would be beyond the scope of the review. In some circumstances, scoping review authors may opt to extract results and map them descriptively.

PRESENTATION OF RESULTS

The findings of a scoping review might be provided as a data “map” in diagrammatic, tabular, graphic, or descriptive form. They can even be mapped in the form of word clouds. Word clouds are a visual representation of data in the form of text. The illustration is such that the importance or significance of a word is depicted with the font size.

We evaluated the effect of the vehicle used to carry calcium hydroxide on postoperative pain levels. A word cloud was generated in an attempt visually present the data collected with the aid of a website https://www.wo rdclouds.com/. The font size of the vehicles used in the word cloud is in accordance with the frequency with which the vehicle is used in various studies to check for posttreatment pain levels.

DISCUSSIONS AND CONCLUSION

This section must provide a thorough analysis of the findings as well as the study’s limitations. In light of current research, practice, and policy, the findings must be evaluated.

Beginning with a broad conclusion based on the facts, this part should move on to more specific conclusions. The resulting conclusion must be in line with the review objective/question. This section should explicitly state the consequences and scope of future research.

CONCLUSION

Scoping reviews play a significant role in laying the foundation for further systematic reviews. They assist in determining the gap in the existing literature, indicating the scope for further randomized control trials.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.