The story behind the synthesis: writing an effective introduction to your scoping review

Scoping reviews are a synthesis of knowledge. Therefore, the introduction’s main purpose is to offer an argument for why we need a synthesis of the knowledge on a particular concept. The Problem-Gap-Hook heuristic [6] can help efficiently lay out this argument.

Let’s begin with the Gap, as it is the same for every scoping review: the lack of synthesis of existing literature. This should be signaled clearly with language such as “Amid such debates, the scholarly community lacks a large-scale, systematic overview of the [arts & humanities] literature” [7] (p 1213) or “there is little evidence on how the Bangladeshi community gain access to diabetes-related information and services” [8] (p 157), or “one area of medical education research that has not yet been systematically examined is family medicine” [9](p 1). It is possible to leave the Gap unstated; readers will be able to infer it as it is similar across scoping reviews. However, making it explicit offers the opportunity to characterize it precisely as Maggio et al. [2] do in their scoping review of HPE scoping reviews (p 690):

the extant research on scoping reviews provides limited information about their nature, including how they are conducted, if they are funded, or why medical educators decide to undertake this type of knowledge synthesis in the first place. This lack of direct insight makes it difficult to know where the field stands and may hamper attempts to take evidence-informed steps to improve the conduct, reporting and utility of scoping reviews in medical education.

Explicitly naming and characterizing the gap is particularly important in a scoping review of scoping reviews, to convince the reader that, amid a sea of reviews, we need another. As scoping reviews proliferate, so too will scoping reviews of scoping reviews, making a strongly characterized gap an essential ingredient of these stories.

While the Gap for a scoping review is invariably some lack of synthesis, this in itself does not justify doing a scoping review. Lots of literature remains unsynthesized; why does it matter in this case? Writers must articulate the Problem that arises because of the lack of synthesis. It is not sufficient to say, for instance, that “Hundreds of knowledge translation (KT) theories exist across a broad range of paradigms including organizational theory, learning theory, and social cognitive theory, but they have yet to be synthesized”. You must make explicit the problem created by an abundance of unsynthesized theoretical KT literature: something like, “Scholars struggle to use KT theory effectively, faced with hundreds of possibilities and no synthesis to guide them”. Look at published scoping reviews to see how other authors express the problem: it might be that the field lacks conceptual consensus, or practices are inconsistent, or controversies remain unresolved, or understanding is inhibited by implicit blind spots, or research is proceeding without programmatic direction. For example, Van Schalkwyk et al. [10] conducted their scoping review of transformative learning as pedagogy because they realized that “understanding of the construct differed amongst us and lacked a clear theoretically grounded comprehension” (p 538); Sebok-Syer et al. [11] argued that a scoping review was needed around measuring interdependence because “variability in both terminology and approaches among researchers may contribute to assessment challenges” (p 1124); and Young et al. [12] declared that, although it has been much studied, “little consensus exists regarding the definition of clinical reasoning” (p 2). Reading critically can help expand your repertoire of phrases for this key part of your Introduction.

The Hook is the ‘so what’ of your scoping review—the statement of why it matters to solve the Problem you’ve identified. The Hook can be expressed either in terms of possibility (e.g., “With a synthesis, we will be able to …”) or caution (e.g., “Without a synthesis, we risk …”). A good scoping review Hook focuses on what the results of the review will be used for, and writers should aim for specific examples of value. Saying that your review will “be useful to a broad audience of educators” is too vague. Be more precise and persuasive. Howell et al. [13] express “an urgent need for a guiding taxonomy of core PRO domains and dimensions in cancer” (p 77); Gottlieb et al. [14] argue that “Given the profound impact of burnout on medicine, understanding imposter syndrome within the context of physicians and physicians in training is critical”(p 117); Maggio et al. [2] set out to “identify areas for improvement in the conduct and reporting of scoping reviews in medical education, thereby helping to ensure that those produced are relevant to and practical” (p 690); and Young et al. [12] assert that “a careful mapping of the concept of clinical reasoning across professions is necessary to support both profession-specific and interprofessional learning, assessment, and research” (p 2). A negative hook, with its articulation of problems or negative impacts associated with not having synthesized the literature, may be particularly effective. If we convert Young et al.’s hook to negative, we get something like “without this careful mapping, learning, assessment and research cannot advance coherently”. Which do you find more compelling?

The Problem, Gap and Hook are important, but they are only three of the sentences in your Introduction. What goes in the other sentences, and how should you organize them?

According to scoping review guidelines [4, 5], the introductory literature review of your paper must do three things: 1) provide relevant details about the “population or participants, concepts, and context” (PCC); 2) establish that there is sufficient literature to warrant a review; and 3) acknowledge any pre-existing reviews and distinguish them from yours. Let’s walk through each of these, unpacking Young et al.’s three-paragraph scoping review introduction as a primary illustration and using additional examples to help you build your Introduction repertoire (Fig. 1).

The final ingredient of an effective introduction is alignment among the “rationale”, “research question”, and “objectives” of the review [3]. These terms are used variably in scoping reviews, reporting guidelines, and reviews of scoping reviews. For our purposes, we use “rationale” to mean why we’ve done a scoping review—what problem does it address? (This is also sometimes referred to as “purpose” in published scoping reviews.) We use “research question” to mean the specific question guiding the search, and we use “objectives” synonymously with “sub-questions” to represent specific foci of inquiry.

Let’s analyze an example where alignment is achieved. Versteeg et al. [19] briefly summarize the literature and land on this statement of the problem: “Overall, the broad range of terms associated with spaced learning, the multiple definitions and variety of applications used in HPE can hinder the operationalisation of spaced learning” (p 206). With this problem in mind, their rationale is “to investigate how spaced learning is defined and applied across HPE contexts”, which they phrase as an overarching question: “How is spaced learning defined and applied in HPE?” (p 206). They then articulate “specific research questions: (RQ1A) Which concepts are used to define spaced learning and associated terms? (RQ1B) To what extent do these terms show conceptual overlap? (RQ2) Which theoretical frameworks are used to frame spaced learning? (RQ3) Which spacing formats are utilised in spaced learning research?” (p 206) This example is well-aligned: “definition and application of spaced learning” remains consistently in focus, and refinements such as “conceptual overlap” and “theoretical frameworks” are further and logical specifications of the overall focus. This example illustrates Levac et al.’s [3] advice to balance broad research questions with clearly articulated scope of the inquiry and link the rationale to the research questions.

Alignment seems straightforward when it is done well, but it can be tricky. Maggio et al. [2] noted room for improvement in the alignment between rationales and research questions in almost 65% of HPE scoping reviews. Echoing Levac et al. [3], they suspected that one reason for this misalignment is “rationales that are applicable broadly to a variety of knowledge synthesis methodologies and not necessarily specific to scoping reviews” (p 695). One strategy for testing your own alignment is to explain why you selected scoping review methodology: as Maggio et al. suggest, tell the reader “what factors influenced [the] decision to undertake a scoping review (e.g., the nature of the literature, the intricacies of the topic, the expertise of their research team, and/or their personal needs such as a graduate student familiarising herself with a topic)” (p 695). Another reason for misalignment is a research question that is too generic and not balanced by clearly articulated objectives that delimit the scope of the inquiry. For example, a generic question like “what is known about medical tourism” cannot support a strong search strategy: the scope needs to be tightened (e.g., medical tourism by Canadians for surgical procedures) in order to focus the work. Finally, even when you try to “balance” a broad question with focused objectives or sub-questions as Levac et al. have advised, be careful that your sub-questions still align with the rationale. If they feel more like detours than logical specifications of the overall focus, then you have a misalignment. For example, a sub-question about the ethics of medical tourism by Canadians for surgical procedures might feel misaligned if the rationale for the scoping review does not have any ethical flavour. Remember: alignment (or its lack) is judged by how well the rationale, question and sub-questions fit the overall story you’re laying out in the introduction—how coherently do they follow from your Problem, Gap and Hook?

A final note on alignment as it relates to the consultation exercise. The consultation is a unique strength of the scoping review. However, differing points of view have been expressed on its optional [20] or essential [3] nature, and it does not appear in the PRISMA-ScR [5] reporting guideline which can leave writers unsure about its role. As you frame the story for a review that included consultation, readers should see this step as aligned and necessary. For instance, you may anticipate a limited literature for scoping and thus seek insights from stakeholder consultation as primary data [15]. You may have scoped an ample literature but identified missing perspectives or voices that you explored using consultation [7]. Or you may use stakeholders to contextualize review findings in order to fully address the question being asked, as in Maggio et al.’s [2] consultation with “seven stakeholders to understand if and in what ways our findings resonated with their experiences conducting scoping reviews” (p 691). The consultation exercise will be described in your methods, but the introduction should set the reader up to expect it. For example, O’Brien et al.’s [16] rationale is to “advance policy and practice for people living with HIV” (p 449), which aligns well with their decision to consult with people with HIV to contextualize the literature and create a patient partner-informed research agenda.

Every scoping review manuscript needs a story to frame the study. This Writer’s Craft offers strategies for telling this story in your introduction (Tab. 1). Use the Problem/Gap/Hook heuristic to establish why we need a synthesis in the first place. Structure the story so that it introduces setting and main characters, establishes that there is sufficient literature for a review, and acknowledges pre-existing reviews. Align the rationale for the work, the research question and the specific sub-questions or objectives—there should be no jarring detours from the storyline. Finally, keep it short: three or four paragraphs should suffice. Your introduction doesn’t need to detail the specifics; it should just sketch the curvature. And don’t worry about ‘giving away’ your results; your introduction is the story, not the synthesis.