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PubMed Searching

Tips for searching NLM PubMed's free database

Creating an Advanced Search

The Advanced Search page can help you build a search with multiple concepts.

 

 

On the Advanced Search screen, you can see your previous searches under History. 

In this example, some of the searches in History have too few results. 
Other searches give you too many results.

 

Combining Search Sets with Boolean

You can combine search sets by clicking the set number under "Search." When you click it, you'll see several choices:

 

Use "OR in builder" to combine search sets which are synonyms - for instance, pregnancy OR prenatal

Use "AND in builder" to add each individual concept to the search - (pregnancy OR prenatal) AND (hypertension or antihypertensive agents)

Use "NOT in builder" to eliminate an idea from your search - (pregnancy OR prenatal) AND (hypertension or antihypertensive agents) NOT animals

 

Using Brackets

Note that bracket placement matters. 
(A AND B) OR (C AND (D OR E))
is different from
(A AND B OR (C AND (D OR E)))

PubMed will read any search from left to right unless otherwise directed by brackets per Order of Operations Rules.

Example: A search for ("early pregnancy" OR "prenatal") AND (surgery OR operation) will return articles on all these topics:


early pregnancy AND surgery
prenatal AND surgery
prenatal AND operation
early pregnancy AND operation

But the same search without the brackets will return results for articles on:


early pregnancy AND surgery
prenatal AND surgery
operation 

The second example finds many more results, because PubMed is finding any article that uses the word operation.