Ovid MEDLINE Search Instructions
Medical Subject Headings (MeSH) and Keyword Searching
What are MeSH terms and why are they important?
All of the articles indexed in MEDLINE have been read by an indexer.
Indexers read each article in order to identify and assign the most
specific terms, from a standardized list of subject terms,
that describe the content of an article. "MeSH" is the acronym
for this master list of standardized Medical Subject
Headings. Usually between 10 and 15 MeSH terms are assigned
to an article to describe its content.
When you type in a search on a topic, you are telling the database to search for articles that have been assigned MeSH terms that match the search term that you entered. If the term you entered is not a standard MeSH term, then the database will not find matches, and your search results may be rather poor. Thus, it is important to make sure that you are searching using the correct MeSH term for your topic.
How do you know what the proper MeSH term is for your topic? The Ovid search interface has a feature to help you find the proper MeSH term. On the main search screen be sure to check the box next to "Map Term to Subject Heading" - this tells the database to provide you with a list of choices of standardized MeSH terms that are associated with your topic. Once you have clicked on the "Perform Search" button, the next screen provides you with a list of MeSH terms so that you can pick a more appropriate term for your topic, if necessary. For example, if you do a search on "high blood pressure" the database will prompt you to choose "hypertension" instead, as this is the recognized MeSH term for that topic. (See Step Two for more details.)
Keyword searching
If you entered a search and the subject heading screen did not retrieve
any MeSH terms that were
relevant to your search, then you need to search using a keyword
search strategy. Keyword searching is often necessary when you are
searching for a medical topic that is very new or if you are looking
for a very specific kind of thing, such as a species name. In these
situations, a MeSH term may not have been assigned. When you search
by keyword (sometimes called searching by textword, or free-text
searching) you are telling the database to search for words that
appear in the title and/or abstract of articles in the database.
(Normally the database would not search this way, rather, it would
search for matching MeSH terms
that have been assigned to each article.)
To search by keyword, uncheck the box next to "Map Term to Subject Heading" on the main search screen, and then proceed to search by entering your search in the search text box. If you started a search with "Map Term to Subject Heading" activated and then realized on the next screen (the subject heading screen) that the database was not able to return any relevant subject headings, then look at the last item in the list of subject headings; this last entry provides an option to search for your term as a keyword. Select this entry and then continue your search.
When you use keyword searching you are searching for the exact words that an author used in the title or abstract, so be aware that different authors may use different terms to talk about the same concept (for example, the following terms could all be used for the same concept: hair loss, balding, pattern baldness, alopecia.) Thus, it is important to think of all possible synonyms that different authors might use to refer to that concept. You will need to search all of these synonyms in order to ensure that you collect a comprehensive set of relevant articles. You can enter multiple terms with an "or" between them in the search text box on the main search screen.
