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Search Basics for the Health Sciences: Combining Search Terms

A guide on basic searching skills that can be applied across databases used for the health sciences

Combining Search Terms

Behind every search in a database or even in Google, there are mathematical operations occurring. While it is not necessary to understand the complex mathematics behind searching, understanding the basic mechanics of the formulas can help you understand how to construct a search. Just like basic mathematics, searching utilizes operators. Instead of [+ - × or ÷], the operators for database searching are: AND, OR, and NOT, known as Boolean operators.


AND combines search terms to retrieve articles that use the major concepts of a search, identified in the PICO(T) process.

The Venn Diagram below represents the use of AND to combine the terms ‘nurse burnout’ and ‘patient satisfaction’. The gray area where the two circles overlap represents the AND as well as the set of articles that the search would retrieve: articles that discuss both nurse burnout and patient satisfaction.

Venn Diagram showing Nurse Burnout AND Patient Satisfaction

Nurse burnout AND Patient satisfaction


OR combines search terms to retrieve articles that use any of the terms that describe a concept or set of concepts or groups you are interested in.

When would I use OR?

OR is important if:

  • multiple terms may describe the population
    • e.g. adolescent OR teenager OR young adult
    • e.g. Native American OR American Indian
  • multiple terms describe the problem
    • GERD OR gastroesophageal reflux
  • you are interested in two different populations
    • physicians OR physician assistants
  • you are interested in several, more narrow, specific aspects of a broader population or problem and don’t want to use the broader umbrella term (e.g. ‘pain’)
    • e.g. back pain OR neck pain
  • You know that multiple spellings, forms or punctuation forms may exist
    • e.g. esophagus OR oesophagus
    • e.g. Ivory Coast OR Côte d'Ivoire
    • e.g. postabortion OR post-abortion

In the Venn Diagram below, the gray area shows that the use of OR gathers all articles that discuss football, hockey or soccer.


Venn diagram showing Football OR Hockey OR Soccer

Football OR Hockey OR Soccer


NOT excludes terms from the set of search results. The use of NOT is generally discouraged, since it can unintentionally exclude relevant articles from your results.

In use, it is represented by the Venn Diagram below, in which the area between ‘sepsis’ and ‘burn’ represents the NOT—in this example, the articles retrieved on the subject ‘sepsis’ would not include articles that discuss sepsis in burns.

venn diagram showing sepsis NOT burn

Sepsis NOT Burn


In actual usage, searches often involve a combination of AND and OR, which may require the use of parentheses. The parentheses preserve the order of operations (remember your algebra!). The words combined with OR live within the parentheses.

E.g. (elderly OR aged OR geriatric)

The concepts from PICO(T) may involve one or several groups of synonyms or alternative concepts. The groups are placed in parentheses, then combined with an AND:

E.g. (elderly OR aged OR geriatric) AND (sleep disturbance OR insomnia OR sleep disorder) AND inpatient

In the database, the parentheses here result in a FOIL operation, so that the search will retrieve articles containing the terms:

  • Elderly AND sleep disturbance         AND inpatient
  • Elderly AND insomnia                      “
  • Elderly AND sleep disorder               “
  • Aged AND sleep disturbance            “
  • Aged AND insomnia                         “
  • Etc.