Inclusion and Exclusion Criteria for a Systematic Review: Examples, Template, and Step-by-Step Guide

A systematic review is designed to identify and synthesise evidence using an explicit, transparent, and reproducible process. One of the most important parts of that process is deciding which studies are eligible for the review. Without clear inclusion and exclusion criteria, researchers can make inconsistent screening decisions, unintentionally select evidence that supports preferred conclusions, or produce a collection of studies that does not actually answer the review question.

Inclusion and exclusion criteria for a systematic review establish these boundaries before studies are selected. They can specify the eligible population, intervention or exposure, comparator, study design, setting, publication characteristics, time period, and other features relevant to the research question. Well-designed criteria are neither unnecessarily broad nor artificially restrictive; they define a body of evidence that is focused enough to answer the question while remaining comprehensive enough to represent the relevant research.

This guide explains how to develop systematic review inclusion and exclusion criteria step by step. It covers the relationship between eligibility criteria and the research question, PICO and related frameworks, common criteria such as population and study design, practical examples, a reusable inclusion and exclusion criteria template, and the correct relationship between eligibility criteria, database search limits, screening decisions, and PRISMA reporting.

What Are Inclusion and Exclusion Criteria in a Systematic Review?

Inclusion criteria are the characteristics a study must satisfy to be eligible for a systematic review. Exclusion criteria identify characteristics that make an otherwise potentially relevant study ineligible. Together, they are usually described as eligibility criteria because they establish the rules used to decide which evidence enters the review.

This is a defining feature of systematic review methodology. The Cochrane Handbook guidance on defining eligibility criteria explains that systematic review authors should pre-specify criteria for including and excluding studies. These criteria should emerge from the review question and should be documented and justified rather than invented after researchers have seen which studies are available.

The distinction between inclusion and exclusion criteria is sometimes presented too rigidly. In practice, many criteria can be expressed from either direction. If an inclusion criterion states that participants must be adults aged 18 years or older, the corresponding exclusion rule is that studies restricted to participants below 18 are not eligible. What matters most is that the rule is unambiguous enough to be applied consistently.

Eligibility criteria should be established from the review question before study selection, not adjusted simply because particular search results are convenient to include or exclude.

Why Inclusion and Exclusion Criteria Matter

Eligibility criteria protect the logical connection between the research question and the evidence being synthesised. If a review investigates an intervention among university students but includes studies of schoolchildren without justification, its final synthesis may no longer answer the original question. Clear criteria prevent this gradual expansion or alteration of scope.

They also reduce subjectivity during screening. Two reviewers examining the same article should ideally be able to apply the predetermined criteria and reach the same eligibility decision. Criteria such as "include high-quality studies" or "exclude irrelevant papers" are too subjective unless quality and relevance have been operationally defined.

Transparent criteria also allow readers and examiners to evaluate the review. PRISMA 2020 requires systematic review authors to specify their inclusion and exclusion criteria and explain how studies were grouped for synthesis. The official PRISMA 2020 checklist places eligibility criteria within the methods section because study selection needs to be reproducible and auditable.

For students undertaking their first systematic review, the criteria should be developed as part of the wider review protocol. Epic Essay's systematic literature review step-by-step guide explains how question formulation, search strategy, screening, quality appraisal, extraction, and synthesis operate as connected stages. Eligibility criteria provide the bridge between defining the question and selecting the evidence.

Start with the Systematic Review Research Question

Eligibility criteria should not be created as an independent checklist after searching begins. They should translate the research question into operational rules. A well-defined review question identifies the concepts that matter and therefore determines what characteristics a study needs to possess before it can contribute relevant evidence.

For intervention reviews, PICO is one of the most familiar frameworks. PICO represents Population, Intervention, Comparator, and Outcome. Cochrane notes that the population, intervention, and comparison components of the review question, together with the eligible study designs, commonly form the basis of pre-specified eligibility criteria.

Other research questions may require different frameworks. Qualitative reviews, exposure-focused reviews, diagnostic questions, and scoping reviews do not always fit a conventional intervention PICO neatly. The framework should therefore be chosen because it clarifies the question, not simply because PICO is familiar.

A hypothetical review question might ask: "Among university students, do mindfulness-based interventions reduce examination anxiety compared with usual support or no intervention?" This question immediately identifies several potential eligibility dimensions: university students as the population, mindfulness-based programmes as the intervention, usual support or no intervention as possible comparators, examination anxiety as the outcome of interest, and an appropriate range of empirical study designs.

How to Convert PICO into Inclusion and Exclusion Criteria

Moving from PICO to eligibility criteria requires greater precision than simply repeating the research question. "University students," for example, may need clarification about undergraduate and postgraduate participants, age restrictions, mixed student populations, and whether students in vocational institutions qualify. Likewise, "mindfulness intervention" needs an operational definition if studies use many related psychological programmes.

The table below demonstrates how a research question can be translated into screening criteria. It is illustrative rather than a universal template, because actual criteria must reflect the purpose and protocol of the individual review.

This conversion makes the screening process more operational. Instead of asking vaguely whether a study is "about mindfulness and students," reviewers can compare it against defined population, intervention, comparator, outcome, and design requirements. That precision becomes particularly valuable when hundreds or thousands of search records need to be screened.

What Criteria Should a Systematic Review Include?

The exact eligibility criteria depend on the review question, but several categories occur frequently. These include population, intervention or exposure, comparator, outcome where appropriate, study design, setting, publication period, language, and publication status. Not every systematic review needs restrictions in every category.

Each restriction should have a methodological or substantive reason. Restricting studies to publications from the previous five years simply to reduce workload may omit important evidence. A time restriction can be appropriate, however, where an intervention, technology, diagnostic definition, policy, or institutional environment did not exist before a meaningful date.

Common eligibility dimensions include:

• Population or participant characteristics
• Intervention, exposure, phenomenon, or condition
• Comparator or control condition where relevant
• Outcome or phenomenon of interest where methodologically appropriate
• Study design
• Research setting or context
• Publication period
• Language
• Publication or report status
• Minimum follow-up period where justified

The list should not become a collection of arbitrary filters. Every additional restriction can remove potentially relevant evidence, so students should be able to explain why it is necessary for answering the review question.

How to Define Population Inclusion and Exclusion Criteria

Population criteria identify who or what the review concerns. Depending on the topic, relevant characteristics can include age, diagnosis, educational stage, occupation, geographical setting, clinical condition, demographic characteristics, or another feature directly connected to the research question. The definition should be specific enough that reviewers can determine whether participants are eligible.

Researchers also need a rule for studies containing mixed populations. Suppose a review concerns adults aged 65 years and older, but a study includes participants aged 50 to 80. The protocol should establish whether the study is eligible when results for participants aged 65 and above are reported separately, whether a particular proportion of the sample must meet the criterion, or whether mixed samples are excluded entirely.

Cochrane specifically recommends planning how studies containing only a subset of eligible participants will be handled. Making this decision in advance prevents inconsistent treatment of mixed-population studies during full-text screening.

Population restrictions also require justification. A review should not exclude participants simply because doing so makes the dataset easier to manage. Restrictions should reflect the review question and the population to which the final conclusions are intended to apply.

How to Define Eligible Study Designs

Study-design eligibility depends on what the systematic review seeks to establish. A review of intervention effectiveness may prioritise randomised controlled trials where such trials are feasible and appropriate. A review of prevalence may require cross-sectional evidence, while a review of experiences or perceptions may require qualitative research.

The design label alone can sometimes be ambiguous. Cochrane therefore recommends defining eligible study designs clearly and, where necessary, focusing on design features rather than relying entirely on labels supplied by authors. A paper may describe itself as "experimental," for example, without satisfying the features required for an eligible randomised trial.

Students should also distinguish primary research from other publication types. If a review seeks primary empirical studies, literature reviews, editorials, commentaries, protocols, opinion pieces, and letters may be excluded because they do not provide the type of primary evidence required for synthesis. Systematic reviews identified during searching can nevertheless be useful for locating additional primary studies even when they are not themselves eligible.

Study design should therefore be chosen because it can provide evidence appropriate to the review question. Selecting only RCTs because they are often described as high-level evidence would be inappropriate for a question about patient experiences, just as qualitative interviews alone would not normally estimate the comparative effectiveness of a medical intervention.

Should Publication Date Be an Inclusion Criterion?

Date restrictions are common in student systematic reviews, but they need justification. A researcher may wish to include studies published between 2015 and 2026, for example, because a major technological, policy, diagnostic, or clinical change occurred around 2015. In that situation, the date boundary reflects the scope of the question rather than convenience.

A date restriction becomes weaker when the only rationale is that older articles seem outdated. Foundational research can remain relevant, and excluding it may alter the evidence base. The researcher should therefore ask whether evidence published before the chosen date could still answer the review question meaningfully.

PRISMA 2020 recommends reporting eligibility criteria concerning characteristics such as publication year and providing rationales for notable restrictions. This transparency allows readers to assess whether the time window could have affected the evidence included in the review.

Students should also distinguish publication date from search date. "Studies published from 2015 to 2026" is an eligibility criterion, whereas "the databases were searched on 10 September 2026" describes when the search was conducted. Both may need reporting, but they serve different methodological purposes.

Should You Restrict a Systematic Review to English-Language Studies?

Language restrictions require careful consideration because they can affect which evidence enters a review. Limiting eligibility to English-language studies may be necessary for some student projects because translation resources are unavailable, but the restriction should be stated transparently rather than treated as methodologically neutral.

Cochrane cautions review authors to consider the implications for bias and equity when restricting eligibility to one language. Relevant studies may have been published in other languages, and their exclusion can affect the completeness or representativeness of the evidence base.

Where an English-only restriction is unavoidable, the methodology should report it and provide an honest rationale. A researcher might explain that only English-language full texts were eligible because translation resources were unavailable within the project. The limitation can then be acknowledged when interpreting the review.

Do not describe English-language restriction as a quality criterion. A study is not methodologically stronger simply because it was published in English. Language and methodological quality are separate considerations.

Should Study Quality Be Used as an Exclusion Criterion?

Students sometimes write "low-quality studies were excluded" as an eligibility criterion without defining how quality was assessed. This creates ambiguity because methodological quality cannot be judged consistently without a specified appraisal framework and decision rule. It can also confuse eligibility screening with risk-of-bias or quality appraisal.

In many systematic review workflows, studies are first selected according to eligibility criteria and then appraised using an appropriate critical appraisal or risk-of-bias tool. Whether studies are subsequently excluded based on a quality threshold depends on the protocol and methodological approach. Any such rule should be established in advance rather than introduced after seeing which studies receive unfavourable assessments.

For example, a review might include all studies meeting its design and population criteria but use risk-of-bias judgements when interpreting or conducting sensitivity analyses. Another protocol may have a justified minimum methodological requirement. What matters is that the approach is explicit and consistent.

This distinction prevents circular screening decisions. Researchers should not label a study "poor quality" merely because its findings differ from the emerging synthesis. Eligibility and appraisal decisions need transparent criteria that operate independently of whether the findings support a preferred conclusion.

Systematic Review Inclusion and Exclusion Criteria Example

A complete eligibility table is often clearer than several paragraphs of disconnected criteria. Consider a hypothetical systematic review examining the relationship between social media use and anxiety among university students. The criteria below demonstrate how the review scope could be operationalised.

The example illustrates an important principle: criteria should be operational. "Relevant studies" would be difficult to apply consistently, whereas specifying university students, social media exposure, and an anxiety measure tells reviewers what evidence qualifies. Actual criteria would need to be adapted to the specific research question and protocol.

Inclusion and Exclusion Criteria Template for a Systematic Review

A reusable template can help students organise eligibility criteria before screening begins. It should be completed using information from the research question and protocol rather than filled with standard restrictions copied from another review. Not every row needs to contain a restriction if that characteristic is irrelevant to the question.

The following template can be adapted for dissertations, systematic literature reviews, evidence reviews, and related research projects.

The rationale column is particularly useful during protocol development because it forces researchers to justify restrictions rather than adding them automatically. It may not always appear in the final dissertation table, but completing it during planning can expose arbitrary or unnecessary criteria before screening starts.

Inclusion Criteria Are Not the Same as Database Search Limits

Eligibility criteria and search limits are related but conceptually different. Eligibility criteria determine which studies qualify for the review. Search filters or database limits determine which records the database retrieves in the first place. Applying an overly restrictive search filter can prevent potentially eligible studies from ever reaching the screening stage.

For example, the protocol may specify that only randomised trials are eligible. A validated study-design search filter may sometimes be appropriate, but a poorly constructed keyword restriction could accidentally remove eligible trials that are indexed differently. Similarly, language, date, and publication-type filters should be applied with awareness of how the database implements them.

A systematic search should therefore be developed to retrieve the relevant evidence with appropriate sensitivity. Epic Essay's guide to researching a literature review explains the importance of using structured search concepts, synonyms, and appropriate scholarly databases rather than relying on a few obvious search terms.

Researchers should report both the search strategy and the eligibility criteria clearly. Readers need to know not only which studies were considered eligible but also how the pool of potentially eligible evidence was identified.

How to Apply Inclusion and Exclusion Criteria During Screening

Eligibility criteria are normally applied during title and abstract screening and again during full-text assessment. The first stage removes records that clearly fail to meet the review scope, while full-text screening allows more detailed eligibility decisions when abstracts do not contain sufficient information. The criteria should remain consistent across these stages.

Before screening a large number of records, it can be useful to pilot the criteria on a small sample. Cochrane recommends pilot testing eligibility criteria because this can expose unclear definitions, improve consistency, and help reviewers apply the rules in the same way. Ambiguities discovered during piloting should be resolved systematically and documented.

During full-text screening, researchers should record a specific primary reason when a potentially relevant report is excluded. "Not relevant" provides little methodological information. More useful reasons include wrong population, ineligible study design, wrong intervention, wrong setting, or another clearly defined criterion from the protocol.

The order in which criteria are assessed can also matter when a study fails several requirements. Cochrane notes that eligibility criteria may be assessed in an order that allows the first failed criterion to serve as the primary reason for exclusion. A consistent hierarchy helps prevent the same type of study being assigned different exclusion reasons arbitrarily.

How Inclusion and Exclusion Criteria Connect to the PRISMA Flow Diagram

PRISMA reporting makes the study-selection process visible. The flow diagram records how many records were identified, how duplicates and other records were removed, how many records were screened, how many reports were sought and assessed for eligibility, and how many studies ultimately entered the review. Reasons for exclusion are reported at the appropriate full-text stage.

Epic Essay's guide to the PRISMA flow diagram explains how identification, screening, eligibility decisions, and final inclusion should be documented. Eligibility criteria provide the rules behind those decisions, while the PRISMA diagram shows the numerical outcome of applying the selection process.

Students should keep screening records from the beginning rather than trying to reconstruct the flow diagram after completing the review. Track the number of records identified from each source, duplicates removed, records screened, reports sought, full texts assessed, exclusions and reasons, and final included studies. Accurate record keeping prevents inconsistencies between the methodology, PRISMA diagram, and final study table.

The inclusion and exclusion criteria explain why a study is eligible; the PRISMA flow diagram shows what happened when those criteria were applied across the review process.

Common Mistakes When Writing Systematic Review Eligibility Criteria

A common mistake is using vague language. Criteria such as "relevant articles," "credible research," or "good-quality papers" leave substantial room for subjective interpretation. Replace them with observable characteristics such as population, design, intervention, setting, or explicitly defined methodological requirements.

Another problem is developing criteria after seeing the search results. A researcher may discover too many papers and respond by imposing an arbitrary five-year publication window, or find too few studies and quietly expand the eligible population. Changes can sometimes be methodologically justified, but they should be transparent and consistent with the objectives of the review rather than being used simply to produce a convenient number of studies.

Students also frequently create mirror-image lists containing unnecessary repetition. If the inclusion criterion is "adults aged 18 years or older," writing "participants under 18" as an exclusion criterion can be useful for clarity, but not every criterion requires repetitive wording. The priority is unambiguous decision-making rather than making the table appear longer.

Finally, researchers may use criteria to exclude difficult evidence without adequate justification. Language restrictions, publication-status restrictions, geographical boundaries, and narrow date ranges can affect the evidence base. A criterion should never be added merely because it makes the systematic review easier to complete. Feasibility matters, particularly in student projects, but methodological compromises should be justified and acknowledged.

A Step-by-Step Checklist for Developing Eligibility Criteria

Eligibility criteria are easiest to defend when they are developed systematically from the review question. Researchers should be able to trace every major criterion back to a feature of the question, intended synthesis, or justified methodological boundary. This creates consistency from protocol development through final reporting.

A practical workflow is:

1. Write a focused systematic review question.
2. Select an appropriate question framework such as PICO or a suitable alternative.
3. Define the eligible population precisely.
4. Define the intervention, exposure, phenomenon, or condition of interest.
5. Specify eligible comparators where the review question requires them.
6. Determine how outcomes will be handled and whether they form part of eligibility.
7. Identify study designs capable of answering the review question.
8. Decide whether setting, date, language, follow-up, or publication-status restrictions are genuinely necessary.
9. Write an explicit rationale for every notable restriction.
10. Decide how mixed or partially eligible populations will be handled.
11. Pilot the criteria on several clearly eligible, clearly ineligible, and uncertain records.
12. Resolve ambiguities before full screening begins.
13. Record specific reasons for exclusion during full-text assessment.
14. Report the selection process transparently using the appropriate PRISMA documentation.

This sequence helps prevent the criteria from becoming an arbitrary list of filters. More importantly, it ensures that the evidence ultimately synthesised remains connected to the question the systematic review was designed to answer.

Writing Clear Inclusion and Exclusion Criteria for a Defensible Systematic Review

Strong inclusion and exclusion criteria make a systematic review focused, transparent, and reproducible. They translate the research question into practical study-selection rules and help ensure that evidence is included because it is relevant to the predefined review scope rather than because its findings are convenient. Population, intervention or exposure, comparator, study design, setting, publication characteristics, and other restrictions should therefore be defined with precision and justified where necessary.

The most reliable approach is to develop eligibility criteria during protocol planning, test them before full screening, and apply them consistently throughout study selection. PICO and related frameworks can help structure the process, while PRISMA provides a framework for transparently reporting the resulting selection decisions. Restrictions involving language, date, publication status, or other characteristics deserve particular attention because they can change the evidence available for synthesis.

Before screening begins, ask whether another researcher could read your eligibility criteria and make substantially the same decision about a candidate study. If the answer is uncertain, refine the criteria further. Clear, pre-specified, and justified eligibility rules create a defensible foundation for the systematic review and make every later stage, from screening and appraisal to synthesis and PRISMA reporting, more coherent.