1. Ovid - Creating a Combined
MeSH and Textword search
Ovid will perform a
combined MeSH match and textword search for you using the Mapping Display screen. As an
example we will work through a search for articles on the treatment of multiple sclerosis.
When you enter a term in the search box, ensure that the Map to Subject
Headings checkbox is selected as shown above. Ovid attempts to match your search string to
a MeSH (Medical Subject Headings) term, and automatically takes you to the Mapping Display
screen to show the matches.
If you want to check the 'children' of the MeSH term (underlined in blue)
then just click on the term, and Ovid will display the MeSH tree. This will allow you to
select some or all of the displayed children.
At this stage, select
the term Multiple
Sclerosis, with
Explode, but not Focus enabled. Also select the "multiple
sclerosis".mp.
option, as this is the Ovid textword search, which will attempt to find your search string
in the titles, abstracts and subject headings fields of the Medline database.
Understanding
Explode and Focus
On the
Mapping Display Screen you will have noticed that Ovid allows you to select Explode and
Focus for each MeSH term.
"Explode"
combines all of the "children" of your selected subject heading with the Boolean
OR operator, together with the MeSH term itself. Using Explode is important because
Medline Indexers strive to use the most specific MeSH term possible. Thus articles indexed
under the MeSH term 'asthma' will not include exercise-induced asthma, because these
articles are indexed under the MeSH term 'Asthma, Exercise-Induced'. If you explode the
term asthma, you will automatically also include articles on exercise-induced asthma.
Exploding ensures more complete coverage (sensitivity), and increases the number of
citations found. However, the search will inevitably be less specific.
"Focus"
is a judgement made by the Medline Indexer that the selected MeSH heading is the main
concept of the article. Select "Focus" to increase specificity (at the expense
of sensitivity), and reduce the number of citations found. The disadvantage of using Focus
is that you are very dependent on the judgement of the Medline Indexer, as to whether or
not the article's focus is on the specified MeSH term.
For an initial search I
would recommend always using Explode, but not Focus. If you find too many references, you
can always repeat the search with Focus enabled. |
