Ovid MEDLINE Search Instructions
Step Three - Exploding and/or Focusing A Subject Heading
The subject heading screen (from Step Two) allows you to explode and/or focus your search.
To explode and/or focus your subject heading, check the appropriate boxes in the columns labeled explode and focus.
Explode
The explode command tells the database to search for your
requested subject heading as well as any more specific terms that
are related to your subject heading. To find out what, if any, narrower
topics are associated with your subject heading (so that you can
decide whether or not you want to explode your heading) click on
the heading itself, this will present a new screen that allows you
to view the narrower (and broader) subject terms associated with
your topic. This screen shows subject headings in a "tree" structure.
You will probably need to scroll down to find your subject heading
in the tree. The plus (+) sign next to a topic means that the topic
has narrower terms associated with it. You can view narrower terms
by clicking on the plus sign. The number of articles that you can
expect to retrieve for each subject heading is provided in parenthesis
after each heading. See the screen image below for an example.
Focus
The focus command tells the database to retrieve only those
articles in which your subject term is considered to be the primary
focus of the article. This will eliminate articles in which your
topic is discussed only peripherally. You will retrieve fewer (but
probably more relevant) articles if you use this feature.
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You can explode and focus at the same time. If you check both the explode and focus boxes next to your subject heading, the database will look for all of the exploded terms and retrieve articles in which any one of the terms has been designated as the main focus of the article. |
Once you have chosen your subject heading and decided whether you want to explode and/or focus, you can move to the next screen by clicking the "Continue" button.
EXAMPLE -- Viewing the "tree" for a subject heading
From the subject heading screen you can click directly on "hypertension" to view its tree - related terms that are more general and more specific. If you choose not to explode hypertension, then you will miss articles that are indexed to more specific forms of hypertension, such as renal hypertension. Instead, you will only retrieve articles about hypertension that do not mention these more specific forms of the disease. (The tree displayed below shows plus (+) signs next to the narrower terms associated with hypertension. These plus signs indicate that there are even narrower topics associated with these headings.)
