Evidence-Based Medicine: Review and Practice: How to search for evidence

Created by Health Science Librarians

Select words from the PICO concepts to guide the development of a PubMed search. Remember:

Start with key concepts.

You do not need to use all of the concepts or all the words from your PICO question as you build your search. Find subject headings if applicable in the database you are using.

Include alternate word endings, especially for key concepts.

List variations of a word, because the database will search for exactly what you type. Use an asterisk to search for words that have the same base but different variations at the end. Don't shorten too much or you may get an error or unexpected results.

For example: (prevent OR preventing OR prevented OR prevention OR preventative)
For example: ed* will return education terms, but it will also give you edema, emergency department, edition, editor, edge, edible, and other unrelated words. educat* will search for education, educating, educator, educated, educational

Include synonyms.

Synonyms will help expand your search and give you more options. Use the word OR between each synonym. Use parenthesis around each synonym group to help the database understand how to organize your search.

For example: (therapy OR therapeutic OR treatment) AND (cancer OR cancers OR neoplasm*)

Include acronyms and alternate spellings.

Include possible acronyms as synonyms for your search terms with OR in between. Beware of acronyms with multiple meanings. Use alternate spellings (such as hematology OR haematology).

For example: "enhanced recovery after surgery" OR ERAS
For example: MI could refer to "myocardial infarction" or Michigan, mile, middle initial, etc.

Use double quotes for phrases.

Search for phrases in double quotes so the database keeps them together as one concept.

For example: "quality of life" or "length of stay"

Apply filters as needed.

Filters, such as article types, gender, or age limits, are usually added after a preliminary search to narrow the results. You can also search for some of these filters with synonyms

For example: (child OR children* OR pediatric* OR teen* OR preteen* OR adolescen* OR youth*)

Your search may need to change depending on the database you use. Some databases, such as PubMed, have a controlled vocabulary. For example, instead of using "cancer" as a MeSH term (a Medical Subject Heading), PubMed uses "neoplasms". When using their controlled vocabulary, you may receive greater accuracy in terms or the topic on which you are searching. Each database has its own set of controlled vocabulary, i.e. subject headings.

See our suggested PubMed Tutorials for assistance and more information.

Example: Building a search

Question: What effect does preoperative carbohydrate treatment, compared with preoperative fasting, have on postoperative recovery in adult patients undergoing surgery?

Click to show the PICO for this question.

P = surgical patients

I = preoperative carbohydrates

C = fasting

O = recovery

Click to show the search for this question.

Search: ("Preoperative Care"[MeSH] OR preoperative OR "pre-operative") AND ("Fasting"[MeSH] OR fasting OR NPO) AND ("Dietary Carbohydrates"[MeSH] OR carbohydrate*) AND ("Postoperative Complications"[MeSH] OR "Recovery of Function"[MeSH] OR recover*)