From your PICO question, select the key concepts and think of any other synonyms or terms an author might use to describe them.

Example: In patients who have experienced an acute myocardial infarction (Population), how does being a smoker (Exposure) compared to a non‐smoker (Comparison) influence mortality rates (Outcome)?

In this example, these are the key concepts and their synonyms:

• myocardial infarction, heart attack
• smoker, smoking
• non-smoker, non-smoking
• mortality, fatality, death

The next step is to combine the search terms in a way the database will understand, using Boolean operators: AND, OR. 

• AND is used in between each different concept
• OR is used in between each synonym of the same concept, with parentheses around each set

Continuing with the example, here is how to use Boolean operators:

(myocardial infarction OR heart attack) AND (smoker OR smoking) AND (non-smoker OR non-smoking) AND (mortality OR fatality OR death)

Boolean operators and parentheses are recognized by almost all databases, so this search strategy structure can be used no matter which database you search.

Are you getting too many results your search? Try the following strategies:

• Add another key concept.
  • Example: (myocardial infarction OR heart attack) AND (smoker OR smoking) AND (non-smoker OR non-smoking) AND (mortality OR fatality OR death) AND (elderly OR geriatric)
• Add limits or filters such as language or publication date
• In PubMed or Ovid Medline, use Clinical Query filters that limit results by the type of question you're asking (therapy, diagnosis, etiology, prognosis, or clinical prediction)

Are you getting too few results your search? Try the following strategies:

• Remove a key concept.
  • Example: (myocardial infarction OR heart attack) AND (smoker OR smoking) AND (non-smoker OR non-smoking) AND (mortality OR fatality OR death) [this indicates that the mortality concept has been removed]
• Add more synonyms or spelling variations if possible
• Truncate terms with an asterisk, such as diabet* for diabetes, diabetic, diabetics, etc