Eligibility Criteria in a
Systematic Review

A systematic review is a rigorous research method that involves collecting, assessing, and synthesizing all the relevant unpublished, and published literature to answer a focused and clearly stated research question. It can take months, or even years, to complete, and involves several steps, from defining the topic to qualitative data analysis in systematic reviews, to finally writing the paper. It is considered one of the most reliable sources of evidence, which is why it is used heavily in evidence-based medicine, and academic research. One of the features that distinguish it from other reviews is its use of eligibility criteria, which determines what studies can be considered in the research.

What Is Eligibility Criteria In A Systematic Review?

Eligibility criteria is a pre-specified, unambiguous basis that determines the scope of studies to be synthesized in a systematic review. The eligibility criteria can be developed newly by the authors, or it can be adopted from another review. In the second scenario, the original authors must be referenced. It guides the selection of literature during the search in databases or other sources. During title, abstract or full-text reading, or potential articles, the criteria dictates what must be included (inclusion criteria), and excluded (exclusion criteria) in the review. These are a fundamental prerequisite of all systematic review methods and are often recorded as a paragraph, or table within the methodology section of the final report.

Eligibility criteria are defined after setting the research question, and study objective(s), and before data collection. However, scoping searches may be performed beforehand to better establish them.

Why Is Eligibility Criteria Important?

Eligibility criteria help to produce more accurate, objective, and meaningful results as they ensure that the literature considered in the systematic review is relevant to the study. If established, and executed correctly, they also reduce the risk of errors and bias in a similar way as other tools, such as a funnel plot in a systematic review. Failing to consistently apply eligibility criteria leads to the inclusion of irrelevant studies in the review which in turn can lead to inconsistent conclusions.

What Should Be Included In The Eligibility Criteria?

Many different factors affect eligibility criteria. However, in general, these should be guided by the systematic review’s research question, the study’s objectives and methodology, and the context of the research itself. They must be sufficiently broad to account for the diversity of studies, and sufficiently narrow to ensure that a meaningful result can be obtained.

Eligibility criteria are often divided into two: the inclusion criteria, and the exclusion criteria.

Inclusion criteria are the elements of a study that must be present for it to be included in the review. Meanwhile, exclusion criteria are the elements of a study that disqualify it from being considered in the research. Even if a study meets all the points stated in the inclusion criteria and exhibits one point in the exclusion criteria, it should be excluded.

Examples Of Eligibility Criteria

Considerations when specifying eligibility criteria include, but aren’t limited to, the following:

• Language of publication (though, ideally, this shouldn’t be limited)
• The year or year range of publication
• Type of publication
• Definition of terms (i.e. the topic, disease, or condition)
• Participants, and any relevant demographic factors in relation to them
• Location or setting of the study
• Types of interventions
• Data or study type
• Study design
• Methodology
• Reported outcomes
• Peer review

Conclusion

Determining eligibility criteria guides the screening and assessment process of systematic reviews, and ensures that the study produces unbiased, and precise results in a transparent manner. With well-established eligibility criteria and a powerful literature review software like DistillerSR, you can automate and simplify your project. It helps manage and configure the review easily to produce audit-ready, and compliant results even faster.