Searching the clinical literature

Identify topics and keywords

Before you start searching, think about your search question and try to identify the distinct topics that exist within it.  You can then break your search down into the keywords which best describe your identified topics. This allows you to clearly specify to the search engine what information you are looking for.

Combine topics

Once you have identified your search topics and decided on your keywords, you need to know how you will combine them in order to find relevant material. The Boolean operators AND and OR are commonly used in databases for this purpose.

AND Search e.g. myocardial infarction AND aspirin only retrieves information which includes both terms.
OR Search e.g. myocardial infarction OR heart attack retrieves all information which includes either terms.


Start with what you feel is your key topic; if you find too few results, use OR to broaden your search and find other similar terms. If you have too many, use AND to bring in other relevant terms and narrow your search.

Use thesaurus terms

Most databases will allow you to search both by typing your own keywords and by using subject terms which have been assigned to the database records. These may be referred to as thesaurus terms, subject headings or MeSH (in Medline and Cochrane). Using thesaurus terms will help you to overcome problems of language and spelling; they are consistent across all records and will pick up different terms (where a condition or procedure may be referred to by more than one name) and different spellings (many terms have both British and American spellings).

Remember that if you are searching by typing in your own keywords, you must think of all alternative terms, synonyms and possible spellings and search for all of them to ensure a comprehensive search.

Decide where to search

Think about where you will begin to search; you may save a lot of time by searching sources such as the Cochrane Library first.  A comprehensive search will have been performed in order to produce the synthesised evidence found in these sources. Therefore, you may not need to perform database searching yourself if you find what you need here.

Evaluate your results

Critical appraisal can help to identify how useful or strong the evidence you find is and addresses how studies or reviews have been carried out and if their methods are appropriate. On the right hand side of this web page you will find several guides and tutorials that will help you gain the skills required to evaluate the clinical literature effectively.