PICO is a mnemonic used to describe the elements of a clinical question. Once a well-structured question is formulated, you will be in a better position to search the literature.
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T - Time/Type of Study (if applicable)
What time periods should be considered? What study types are most likely to have the information you seek?
Use Medical Subject Headings (MeSH) to identify the best keywords to use in your search statement:
For more information about MeSH, view this tutorial from the U.S. National Library of Medicine.