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Select, Collect, & Synthesize

Eligibility Criteria | Screening | Using Covidence | Risk of Bias | Data Collection | Data Synthesis

At this point, you have finalized your research question and selected the type of evidence synthesis review that best fits your question, timeline, and purpose. You have also written your protocol and the literature searches were completed by a librarian.

Here we cover what to do next in your evidence synthesis review.

Eligibility Criteria

What It Is | Examples | Manuals & Guidance

What It Is

Eligibility criteria, also called inclusion and exclusion criteria, are based on your research question. They guide the selection of studies.

Clearly define your eligibility criteria to reduce misunderstandings by your review team members.

Include elements of your research question such as:

  • Population
  • Intervention, exposure, or concept of interest  
  • Outcomes
  • Study design (e.g., randomized controlled trial, cohort study, case series)
  • Setting (e.g., primary, specialty, inpatient, nursing homes, long-term care setting)

Criteria may also describe report (article) characteristics:  

  • Publication year
  • Language
  • Article type (e.g., original research, review, preprints)

Include the rationale for criteria used to limit study inclusion. For example, if you limit to studies published from 2014 to the present because a diagnostic test that you are investigating was only introduced in 2014, explain this in your protocol and review (Shamseer, 2015).

Examples

You can write eligibility criteria as a paragraph, bulleted list, or in a table. What is important is that you describe in detail what each criterion means and specify what it does or does not include. This ensures consistent application of the criteria and avoids misunderstandings by the review team.  

Example: In the literature, authors use many different words to describe “cancer-related fatigue”. For a review on this topic, you need to define what “cancer-related fatigue” means for your review and specify which of the different words authors used are acceptable.

You might use the National Comprehensive Cancer Network definition for cancer-related fatigue. You specify only tired, tiredness, and exhaustion are other acceptable words (e.g., synonyms) for fatigue.  

To find examples of eligibility criteria, refer to the resources listed below or look at published reviews on your topic of interest. The two examples below include some of the considerations described earlier about selecting your criteria (e.g., using definitions, clarifying acceptable terms, etc.).

Example: Systematic review 

In pregnant people, what is the impact of access to cooling centers during heat waves on premature birth? Or does the use of cooling centers during heat waves reduce premature births?

Inclusion criteria:
  • Population: pregnant people (adults 18 years and older)
  • Intervention: Cooling centers (a public or private building or room with cooled air circulated via fans, air conditioning, or other methods to provide temporary relief from heat conditions)
  • Exposure: Heat wave (A heat wave is a period of abnormally hot weather generally lasting more than two continuous days) Source: NOAA  
  • Outcome: premature or preterm birth (Preterm is defined as babies born alive before 37 weeks of pregnancy are completed. Any sub-category of gestational age may be included. The preterm birth may occur because of spontaneous preterm labour or because there is a medical indication to plan an induction of labour or caesarean birth early.) Source: WHO  
  • Publication year: 2000–2024
  • Article type: original research, reviews (all types), conference abstracts/proceedings, preprints, white papers/technical reports
  • Species: Humans
  • Geographical location: United States or Canada
Exclusion criteria:
  • Population: Pregnant people not included in the study or data on pregnant people cannot be separated from other populations
  • Exposure: Heat wave was shorter than 2 continuous days
  • Intervention: cooling center data not separated from other interventions used during the heat wave
  • Outcome: Babies were born after 37 weeks or stillbirth
  • Geographic location: United States or Canada data not reported separately if multiple countries included
  • Article type: commentary, opinion, letters, dissertations,

Example: Scoping review 

What research has been conducted on the impact of extreme heat on fertility?

Inclusion criteria:
  • Population: adults 18 years and older
  • Exposure: Extreme heat – “Extreme heat is a period of high heat and humidity with temperatures above 90 degrees for at least two to three days.” (Source: ready.gov)  
  • Acceptable synonyms: extreme heat, extreme temperatures, heat wave, heat stroke, heat-related illness, heat exhaustion
  • If length of time or temperature is not reported in abstract, but “extreme heat” is, include at title and abstract and determine at full text screening.
  • Outcome: fertility – “ability to produce or conceive children” (Source: NCI)      
  • Acceptable synonyms: fertility, fertile, infertility, infertile, live births, conceive, pregnancy, pregnant
  • Publication year: 2000–2024
  • Article type: original research, reviews (all types), conference abstracts/proceedings, preprints, white papers/technical reports, dissertations
  • Study design: all
  • Species: Humans
  • Geographical location: international
Exclusion criteria:
  • Population: children/pediatrics, individuals less than 18 years old
  • Exposure: extreme heat event was shorter than 2 continuous days and/or temperature not reported (as Fahrenheit or Celsius)  
  • Outcome: fertility not focus of study
  • Article type: commentary, opinion, letters

Manuals & Guidance

For more details and guidance on selecting your eligibility criteria based on type of review and question, please see these resources. You can also ask a NIH Librarian for additional help.

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Eligibility Criteria | Screening | Using Covidence | Risk of Bias | Data Collection | Data Synthesis