Savvy Searcher
Advanced Search Techniques
As you become more comfortable searching medical literature
databases like MEDLINE, you realize the value of searching
by MeSH terms. Using the Ovid interface's mapping feature
or PubMed's MeSH Browser, identifying the best MeSH term is
usually easy. These features permit you to type the topic
as you know it, and will provide you with a list of MeSH terms
to choose from.
Sometimes though, the mapping feature and MeSH browser don't
provide MeSH terms that quite describe the information that
you want. This can occur when you're researching a complex
topic that is represented by coordinating several MeSH terms
and also when the topic is so new that MeSH terms don't yet
exist to define it. What can you do to find the information
that you need when this happens? The following are some search
tips that can help you narrow your search to the information
that you need.
The examples below illustrate the tips using the Ovid interface
and MEDLINE. Many alternate search interfaces will provide
equivalent capabilities; check the "Help" information when
you use an alternate search interface. These tips can also
be applied to any database that uses a controlled vocabulary
like MEDLINE with its MeSH vocabulary (examples: CINAHL, CINAHL,
PsycINFO, etc.).
Field Searching
Field searching in Ovid allows you to bypass the mapping
and subheadings screens to locate your terms in a specific
field. For example, consider a case where you're interested
in identifying articles on coronary heart disease and nutrition.
Rather than finding the MeSH terms for these topics, you could
search for these terms in specific fields of the record. Usually,
searching by field works best when you start by trying to
find articles with your terms in the title field, then moving
on to the abstract field if necessary.
On the screen above you see the results of searching for
the terms coronary heart disease and nutrition in the title
of the article (ti) and the abstract (ab). This is done by
adding a period plus the code for the field (ti for title
and ab for abstract) after the term. In this case, the terms
were also enclosed in parentheses because the searched checked
for two terms. The first search which was limited to the title
of the article is a smaller set of more focused search results;
articles on this topic are likely to have these words in the
title.
The second search which checks for these terms in the abstract
of the article is a larger and less focused set; articles
on this topic are likely to have these words in the abstract,
but a number of irrelevant articles will also have these words
in the abstract.
Some additional useful field codes are:
au Author
in Institution
jn Journal name
A list of all field codes and a screen for selecting fields
for a search can be found by using the "Search Fields" icon
represented by a magnifying glass on the Main Search Page.
Truncation
Truncation is a tool that can be used in combination with
field searching in order to find a word with multiple endings
or variant spellings of words. For example, consider a case
where you are interested in finding information on weight
loss and the heart. You'd like to include variations of the
more medical term 'cardiac,' and want to include articles
that mention cardiac, cardiovascular, cardiology, cardiorespiratory,
etc. To find all variants, you could take the base of the
word "cardi" and add the unlimited truncation symbol, the
dollar sign ($), so that the system finds words that begin
with"cardi" and end in any way.
When you look at the results of this search, you see that
number of variations of "cardi$" appear in the results.
You can also use truncation within a word for cases where
there may be several spellings of one word. This is particularly
useful in cases where you want to include both the American
and British English spellings. For example, to find articles
that mention "ischemic" or "ischaemic" in the title, you can
use the question mark (?) which indicates that one or no characters
can occur at that position. The question mark can be used
in the middle or at the end of a word.
As you look at the results, you should see examples of both
the British and American English spellings.
Some additional useful truncation symbols are:
|
# |
Used to substitute for one required letter. For example,
wom#n will find both women and woman. |
|
$n |
Used to indicate the maximum number of letters at the
end of a word. For instance, cardi$3 will find words
that begin with "cardi" followed by up to three more
characters. This search would find instances of cardiac,
cardio, and cardial, but not cardiorespiratory or cardiovascular. |
Finding additional articles
While field searching and truncation can be used as alternatives
to searching by MeSH, you may get the best results by using
these techniques to help you find the best MeSH terms for
a particular topic. Another way to approach this is to use
field searching and truncation to locate one perfect article,
and then follow the leads provided by the MeSH terms to locate
more articles like it.
For example, in the first search we searched for "(coronary
heart disease and nutrition).ti" and found a number of articles
including a great review article:
5. Pandya DP. Nutrition & coronary heart disease. [Review]
[70 refs] [Journal Article. Review. Review, Tutorial] Comprehensive
Therapy. 24(4):198-204, 1998 Apr. Himmelfarb Library has partial
holdings UI: 98260654
To find more articles like this one, click on "Complete
Reference" to see which MeSH terms are attached to it.
The MeSH terms that describe the main topic of the article
are marked with an asterisk (*). To find more articles like
this one, you could jot down the best MeSH terms and try different
combinations of these terms in new searches.
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