OVID Medline Guide
Choosing Subject Headings
This example outlines the steps involved in searching for journal articles about the use of vitamin c for preventing and controling the common cold:
Enter the term vitamin c in the search box as below, then click on the Perform Search (click on the play button below to see this action)
You may have noticed that the Map Term to Subject Heading box is ticked by default. This will link the term to the appropriate Subject Heading, if one exists.
Medical Subject Headings (MeSH) is a list (thesaurus) of keywords or descriptors that describe articles in Index Medicus and MEDLINE. Indexers scan an entire article and assign up to twenty MeSH terms to each article. The MeSH terminology provides a consistent way to retrieve information that may use different terminology for the same concepts.
The Mapping feature is designed to lead you through the Medical Subject Indexing system without necessarily having any prior knowledge of MeSH Subject Headings. The next screen will contain the MeSH term that Medline mapped to:
Medline Mapped to the term Ascorbic Acid. This is the term used in MeSH for vitamin C.
What the Explode button does
When you select the Explode box you will retrieve records the subject heading listed and also any or all more narrow or specific terms taken from the thesaurus. This means that Explode will increase the number of records you retrieve. The preferred first search usually includes the Explode option. The reason for this is that you can't always be sure if the article that best suits your needs is indexed as the main Subject Heading or perhaps indexed as a narrower term. If you omit the Explode option from your search you will miss the narrower terms for the concept.
What the Focus button does
When you select the Focus box it will restrict your search to those records where the concept listed is the main point of the article.
If you choose to click on the term itself the link will take you to the MeSH thesaurus (called a Tree) where you can view the narrower and broader terms yourself.
In the example above we will choose the Explode option (to include all the narrower terms) and then continue: