You have probably noticed when searching in databases or using Google, that when you enter your terms surrounded by quotation marks - like, "kidney failure" - you get slightly different results than if you entered the term with no quotes.
This is because quotation marks are used for phrase searching. Phrase searching works a little different in PubMed than in other databses; lets take a closer look:
- When you surround your search terms with quotation marks, you are telling the database that the words must appear as an exact phrase.
In PubMed the following searches break down like this:
kidney failure = 161,894 results
"kidney failure" = 80,598 results
- Searching for the terms with no quotation marks gives us results that contain synonyms and MeSH terms.
This "automatic term mapping" includes results that include kidney, renal, failure and insufficiency in any combination.
- We get fewer results with "kidney failure" because all the results contain the exact phrase.