Defining the Scope of a Literature Review

Define the scope of a literature review by setting the boundaries that determine which evidence is eligible: the topic and concepts, and—when relevant—the population, setting or geography, time period, and study or source characteristics. Tie each boundary to the review purpose and research question, convert it into explicit inclusion and exclusion criteria, and keep the scope only when the resulting evidence is aligned, sufficient, and feasible; otherwise narrow or broaden the specific boundary causing the mismatch.

Literature review scope planner

Use the scope as a sequence of decisions: define the review need, set only boundaries that affect relevance or feasibility, turn them into eligibility rules, then test whether the result is workable.

1. 1
   Anchor the review.
   State the review purpose and research question so every later boundary has a reason.
2. 2
   Set relevant boundaries.
   Define concepts and, when they matter to the question, population, setting or geography, time period, and study or source characteristics.
3. 3
   Operationalise the scope.
   Translate each justified boundary into paired inclusion and exclusion criteria that make eligibility decisions explicit.
4. 4
   Test workability.
   Check question alignment, evidence sufficiency, and feasibility together before treating the scope as settled.

Keep

Relevant literature is coherent and sufficient for the intended synthesis, and the planned depth is feasible.

Narrow

The current boundaries admit evidence that is too heterogeneous, remote, or difficult to synthesise around the question.

Broaden

A specific restriction repeatedly excludes pertinent evidence needed to answer the research question.

There is no universal correct breadth: a workable range depends on the review purpose, evidence base, and project constraints, so restrictions should be added only when they materially improve relevance or feasibility.

What a Literature Review Scope Needs to Define

A literature review scope is formed by several boundary dimensions that jointly control eligibility.

Scope dimensions can include the topic and concepts being examined, the population, setting or geography in context, the relevant time period, and applicable study characteristics and source characteristics.

Which dimensions need explicit limits depends on the review purpose and the evidence needed to address it.

Each boundary dimension affects which literature is relevant and eligible for inclusion.

Conceptual boundaries limit the topic and concepts; contextual boundaries can limit the population, setting, or geography; and evidence and time boundaries can limit the time period, study characteristics, or source characteristics.

These scope criteria should work together coherently so that eligibility reflects the intended coverage rather than a set of disconnected filters.

Source characteristics define eligibility here, while source quality is a separate evaluative issue.

Topic and Conceptual Boundaries

Conceptual boundaries identify which concepts, constructs, theories, phenomena, relationships, or sub-areas belong to the intellectual focus of a topic.

Included core concepts define the evidence domain that is relevant to the review question, while adjacent concepts may be excluded when they fall outside that focus.

Each conceptual limit therefore establishes a condition for whether literature is relevant to the review's intended coverage.

Tightening or relaxing a conceptual boundary changes which evidence qualifies as relevant.

For example, a broad topic such as remote work could be focused on the core concept of employee productivity, while adjacent concepts such as employee wellbeing or organisational culture remain excluded unless the review question requires them.

Expanding the conceptual scope to include employee wellbeing would make literature examining that construct relevant even when productivity is not its primary focus.

Conceptual boundaries therefore distinguish included core concepts from adjacent concepts that may relate to the topic but remain outside the chosen sub-area.

Population, Setting, and Geographic Boundaries

Population, setting, and geographic boundaries define whose evidence, which environments, and which locations are relevant when those differences affect the review question.

Population criteria determine which participants or participant characteristics affect eligibility, setting defines the context in which evidence needs to apply, and geography limits location when regional conditions affect applicability or comparability.

These boundaries should be applied only when the distinction can materially change which evidence addresses the review question.

• Population: Include or exclude participants according to characteristics that matter to the review question; a population boundary is unnecessary when those characteristics do not change relevance.
• Setting: Limit the evidence to a particular environment or context when findings need to apply within that setting; otherwise, a setting restriction may exclude applicable evidence without justification.
• Geography: Use a location or regional boundary when environmental or system-level differences affect comparability; location alone is not sufficient reason to exclude evidence.

For example, a review concerned specifically with healthcare delivered in rural clinics may need a setting boundary if evidence from other care environments does not address the same context.

Population, setting, and geography therefore function as conditional eligibility criteria rather than restrictions that every literature review must use.

Time Period, Study Characteristics, and Source Boundaries

Evidence boundaries determine which time period, study characteristics, and source characteristics are eligible for consideration in a literature review.

A date range limits evidence by publication period, while study design or methodology and source characteristics such as publication type or language can qualify or exclude evidence according to the intended scope.

Each restriction requires a rationale when it materially affects whether evidence can address the review question.

A time period should reflect a relevant temporal requirement rather than an arbitrary assumption that newer evidence is better.

Study characteristics may limit eligibility to a study design or methodology needed to answer the review question, while source characteristics may specify an appropriate publication type or document type.

Language can also function as an eligibility criterion when a justified practical or evidence-base requirement makes the restriction necessary.

The appropriate condition therefore depends on the review question, field, evidence base, or practical requirement.

Eligibility determines whether a source fits the scope; later appraisal of source quality is a separate task.

How to Set the Literature Review Scope Step by Step

Set the literature review scope by moving from the review purpose and research question to explicit boundaries, translating those boundaries into inclusion criteria and exclusion criteria, and then testing whether the resulting scope is feasible.

The sequence provides planning checkpoints rather than a rigid one-pass workflow, because the available literature or practical constraints can require earlier decisions to be revisited.

The intended purpose of the literature review should therefore be clear before boundaries are chosen, so each limit supports the contribution the review is intended to make.

1. Define the review purpose and research question. Specify the intended contribution and focus; check that the question is clear enough to guide boundary setting.
2. Set the boundaries. Decide which relevant conceptual, contextual, temporal, study, and source limits apply; check that each boundary has a reason tied to the question.
3. Translate boundaries into eligibility criteria. Express the limits as explicit inclusion criteria and exclusion criteria; check that they make eligibility decisions sufficiently clear.
4. Assess breadth against the available literature. Determine whether the boundaries leave an unmanageable volume of relevant literature or too little evidence to address the question; narrow or broaden the scope when needed.
5. Check feasibility. Confirm that the resulting scope is workable within the review's practical constraints; revisit an earlier boundary when feasibility remains mismatched with the intended purpose.

Scope refinement can be iterative when the available literature shows that the initial boundaries are too broad or too narrow for the intended review.

In that case, revisit the relevant boundary, narrow or broaden it with a clear rationale, and check feasibility again rather than treating the initial scope as fixed.

Anchor the Scope to the Review Purpose and Research Question

The scope should serve the review purpose and make the research question answerable by keeping the evidence focused on the intended contribution.

The review purpose establishes what the review is trying to accomplish, while the research question constrains which evidence is relevant to that objective.

Boundaries should therefore support the intended answer rather than introduce limits that are unrelated to the question focus.

Question elements can imply different scope boundaries depending on the field, review objective, and available literature.

Concepts may define the intellectual focus, population and context may narrow where the evidence applies, a time period may limit temporal coverage, and evidence characteristics may constrain which forms of evidence are eligible.

These dimensions are conditional rather than a universal question framework; detailed work to formulate the review question is a neighbouring task rather than part of scope alignment.

A vague or overextended question can leave the scope unstable, while an excessively restrictive question can narrow the boundaries until too little relevant evidence remains for the intended review.

• Concepts: The concepts named or implied by the question define which topics and relationships belong within the focus.
• Population and context: Relevant participant, setting, or geographic conditions can imply boundaries when they affect which evidence can answer the question.
• Time period: A temporal focus can imply a date boundary when evidence from outside that period does not serve the intended question.
• Evidence characteristics: Required forms of evidence can imply limits on eligible study or source characteristics when those distinctions are necessary for the intended answer.

Turn the Scope Into Inclusion and Exclusion Criteria

Inclusion criteria and exclusion criteria convert abstract scope boundaries into explicit eligibility rules for deciding which studies or sources qualify and which do not.

Inclusion criteria state the conditions evidence must meet to qualify, while exclusion criteria state the corresponding conditions that disqualify evidence from the defined scope.

The table translates justified scope boundaries into paired eligibility decisions rather than source-quality judgments.

Each rule should map to a relevant scope dimension and have a rationale tied to the review objective.

For example, if the chosen population boundary is adults, the inclusion rule can require adult participants and the corresponding exclusion rule can disqualify studies limited to children; both rules operationalize the same population boundary.

The appropriate criteria may involve population, concept, setting, geography, time period, study characteristics, publication type, or language only when those boundaries are justified.

These eligibility criteria can subsequently inform how researchers plan the literature search without treating eligibility rules as search syntax or source-quality scores.

Narrow or Broaden the Topic to a Workable Range

Narrow the topic when the current scope admits too much heterogeneous or loosely relevant literature, and broaden it when existing restrictions exclude evidence needed to answer the research question.

Keep the scope unchanged when the relevant literature is sufficiently coherent and adequate for the intended review.

The decision should depend on relevance, coherence, and evidence sufficiency rather than on raw search-result counts.

• Narrow: Tighten one or more boundaries, such as concepts, population, setting, geography, time period, or study characteristics, when the current scope includes material that is too diffuse for the question. Tightening a boundary should increase focus and reduce the volume of less relevant evidence.
• Broaden: Relax a boundary when the current scope excludes relevant literature needed to address the question. Relaxing limits on concepts, population, setting, geography, time period, or study characteristics can increase coverage when the existing restriction is unnecessarily limiting.
• Keep: Retain the current boundaries when they admit enough relevant literature with sufficient coherence to support the review question. A boundary should not be changed merely to alter the number of retrieved studies.

For example, a topic covering workplace wellbeing across all occupations and settings may become more workable by narrowing the population to healthcare workers when that population is central to the research question.

Conversely, a scope limited to one narrowly defined workplace setting may need to broaden the setting boundary if that restriction excludes relevant literature needed for the intended answer.

After tightening or relaxing a boundary, recheck that the revised scope remains aligned with the research question and still contains sufficient relevant literature.

How to Check Whether the Scope Is Workable

A workable literature review scope must satisfy three conditions together: it should fit the research question, contain enough relevant literature for the intended synthesis, and remain feasible within the project constraints.

Signs the Scope Is Too Broad

A scope is too broad when its boundaries admit more conceptual or contextual variation than can be synthesized coherently for the research question.

Excessive breadth may manifest as heterogeneous evidence, remote subtopics, conflicting lines of inquiry, or unclear boundaries for relevance and inclusion criteria.

These signals should be interpreted together because no single manifestation proves that the scope is overbroad.

• Heterogeneous evidence: Evidence addresses substantially different concepts, populations, settings, or periods, making a coherent synthesis difficult. This may indicate that one or more conceptual or contextual boundaries need tighter definition.
• Remote subtopics: Large parts of the literature are only indirectly related to the intended focus, which can dilute relevance. This suggests that the concept, population, setting, or geography boundary may be wider than the research question requires.
• Conflicting lines of inquiry: The scope contains distinct questions or evidence streams that cannot be integrated around one clear analytical focus. This may indicate excessive conceptual breadth rather than meaningful diversity within one coherent question.
• Unclear boundaries: Inclusion criteria cannot be stated consistently because it is unclear which studies or sources belong inside the review. This suggests that the scope boundaries themselves require clearer definition before evidence can be selected consistently.
• Large result set: A high volume of search results can support the diagnosis when the retrieved literature is also heterogeneous or weakly related, but result count alone does not prove that the scope is too broad because retrieval strategy can also inflate the volume.

For example, a review that covers employee wellbeing across unrelated industries, populations, organisational settings, and outcomes may be too broad if those differences produce disconnected lines of inquiry that cannot answer one coherent research question.

By contrast, a broad review can remain workable when its diverse evidence still addresses the same defined focus with clear relevance and inclusion boundaries.

In that case, breadth alone does not indicate that tighter boundaries are needed.

Signs the Scope Is Too Narrow

A scope is too narrow when restrictive boundaries exclude relevant literature needed to answer the research question or support the intended synthesis.

Excessive restriction can leave an evidence base that is too limited because pertinent evidence falls outside the chosen concepts, population, setting, geography, time period, study characteristics, or other exclusion criteria.

A small evidence base alone does not establish that the scope is too narrow, because an emerging topic or genuinely narrow question may legitimately have limited literature.

• Repeated exclusion of pertinent evidence: Studies that are relevant to the research question repeatedly fail the inclusion criteria because of the same restrictive boundary. This may indicate that the affected conceptual, population, contextual, temporal, or study-characteristic boundary is narrower than the intended question requires and could justify broadening that condition.
• Evidence cannot support the intended synthesis: The included evidence addresses only a restricted part of the research question, leaving an important part of the intended synthesis unsupported. This may indicate that a boundary excludes relevant literature needed for the review rather than simply improving focus.
• Question specificity exceeds the available evidence: A combination of narrowly defined concepts, population, setting, geography, time period, or study characteristics can leave too little relevant literature to address the question as framed. Relaxing the boundary responsible for the restriction may broaden the evidence base while preserving the question's intended focus.
• Low literature volume: Finding few relevant studies is a weaker signal because scarcity can reflect either restrictive boundaries or a genuinely limited evidence base. If the topic is emerging and the available literature is naturally sparse, preserving the narrow scope may represent the evidence more accurately than broadening it solely to include more sources.

For example, broadening may be justified when a setting restriction repeatedly excludes otherwise pertinent studies needed to answer the research question.

If comparable evidence remains scarce after that restriction is considered because the topic itself is emerging, the limited evidence base may reflect legitimate narrowness rather than a scope problem.

The diagnostic task is therefore to identify which specific boundary is excluding relevant evidence before deciding whether that boundary should be relaxed.

Check the Scope Against the Review Question, Available Literature, and Project Constraints

Final scope validation should verify that the proposed boundaries align with the research question, provide sufficient relevant literature for the intended synthesis, and remain feasible within the project constraints.

These conditions need to hold together because intellectual fit does not by itself establish evidence sufficiency or practical feasibility.

The final scope check therefore tests fit and feasibility without imposing a universal source count or required page count.

• Research question alignment: Verify that each major boundary helps define evidence capable of answering the research question. If a boundary excludes evidence needed for the intended answer or admits material outside the question's focus, revisit that boundary.
• Relevant literature: Verify that the available literature within the boundaries is relevant and potentially sufficient for the intended synthesis. If pertinent evidence is repeatedly excluded, reconsider the eligibility rules or boundary responsible rather than assuming that the evidence base itself is inadequate.
• Evidence availability: Verify whether limited literature reflects the evidence base rather than an unnecessarily restrictive eligibility condition. If that distinction remains uncertain, revisit the relevant boundary or eligibility rule before treating scarcity as evidence that the scope is unsuitable.
• Time and depth: Verify that the planned coverage and expected depth can be handled within the time and other project constraints. If the required depth cannot realistically be achieved across the current scope, revisit the boundary contributing to excessive coverage.
• Access and requirements: Verify that the evidence required by the scope can be accessed and that the planned coverage fits applicable assignment or project requirements. If access or requirements make a boundary impractical, revise the affected condition while preserving alignment with the research question.

A failed check identifies a boundary or eligibility rule that may require revision rather than proving that the whole scope is invalid.

Evidence sufficiency and feasibility remain conditional on the review purpose, available literature, expected depth, access, and project constraints.

The scope should also remain compatible when researchers select the review method, without using scope validation to determine the method itself.

Example of a Clearly Defined Literature Review Scope