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Mastering Keyword Searching

Using Limits and Inclusion/Exclusion Criteria

Once you have some search results, you will need to decide which articles you will actually use in your literature review. This can be done using filters/limits in the databases, applying inclusion/exclusion criteria, and appraising the articles.


The databases can help you narrow down your search results by criteria such as publication year, language, age group, and publication type. This feature, which is called Filters or Limits, usually appears to the left of the search results, such as in PubMed and CINAHL. In Ovid/PsycInfo, the limits option is located above the search results. (See the Searching with Library Tools tab for tutorials.)

Inclusion/Exclusion Criteria

Usually, filters/limits are not enough criteria to narrow down your results to only the best, most essential evidence. The final step in deciding which articles to review is to apply Inclusion Criteria. If a study meets your inclusion criteria, then it would be an appropriate piece of evidence to help answer your PICO(T) question. If a study meets one or more of your exclusion criteria, it will not help answer your PICO(T) question and you can discard it. You will have to read titles and abstracts to determine if articles meet your inclusion criteria.

Examples of Inclusion Criteria

Using criteria like these examples will help you decide if a study will answer your PICO(T) question. Some of these also fall into the Limits or Filters category.

  • PICO(T) or Major Topic Elements: Is the article actually talking about your topic? Do the outcomes or study population match closely enough to those you are asking about in your research question? If one of these elements is different in the study from your question, you may need to exclude it. This is another way of asking whether the article is actually relevant.

  • Age: Are you working with a specific age group? The study should include subjects that are within your specified age range.

  • Setting: Are you looking for studies in a specific setting? i.e. home, outpatient, inpatient, etc.

  • Health Status: For example, this could be patients with good or poor prognosis.

  • Study Design Preference: Are you looking for RCTs only? Will you also include other types of trials or cohort studies?

  • Size of Study Groups: What is the minimum study group size you are willing to consider?

  • Study Drop Out Rate: Are you looking for studies with drop out rates <20%? <10%?

  • Year Range: Studies published within the last 5 years? 10 years?

  • Language: Studies published in English? Other languages?

Exclusion criteria is the inverse of your inclusion criteria. For instance, if your inclusion criteria for study drop out rate is <20%, the exclusion criteria would be a drop out rate of >20%. 


Once you have chosen the studies that have potential to answer your question, you can then evaluate them for things like validity, reliability and quality.

Adapted from Evidence-Based Practice for Nursing: Evaluating the Evidence and Evidence Analysis Manual

Filters and Limits

Inclusion and Exclusion Criteria