2. Using Subject Headings
LITERATURE SEARCHING
Conducting a topic-based search of the OvidSP
databases available via the NHS Scotland
Knowledge Network
These guides are designed to facilitate self-study, or to accompany a librarianled session on searching for information via the OvidSP databases.
Written by Seona Hamilton. Please contact your local library or subject librarian for training in literature
searching and using online databases.
Last updated June 2011
1
Using Subject Headings
Most databases index each individual article with a number of subject headings which describe
their content. These are very useful for searching for articles by subject.
Subject headings are based on a controlled language and differ between databases. For
example, Medline uses MeSH (Medical Subject Headings) whereas CINAHL uses its own
controlled language which has far more terms specific to nursing.
How the National Library of Medicine indexers assign MeSH
The indexer will examine the article and assign up to 15 subject headings from the MeSH
controlled vocabulary that best describe its content. They will try to include:
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The topic of the article
The age group of the population studied, if relevant
The nature of the study (e.g. Human or Animal, Male or Female) if relevant
The publication type (e.g. Clinical Trial, Review) if relevant
Sometimes the indexer will also assign a subheading to a particular MeSH term to show that a
particular aspect is being looked at (e.g. diagnosis, pathology, therapy)
EXAMPLE:
Anderson, T. Prostaglandins for the prevention of PPH
Practicing Midwife 8(7) 43-5 2005
The above article was allocated the following subject headings by Medline:
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Drug Therapy, Combination
Female
Humans
Labor Stage, Third / de [Drug Effects]
Midwifery / mt [Methods]
*Misoprostol / tu [Therapeutic Use]
*Oxytocics / tu [Therapeutic Use]
Oxytocin / tu [Therapeutic Use]
Postpartum Hemorrhage / nu [Nursing]
*Postpartum Hemorrhage / pc [Prevention & Control]
Pregnancy
*Prostaglandins / tu [Therapeutic Use]
Treatment Outcome
13 MeSH terms were used to describe the article, including terms that showed that the article
addressed the treatment outcome of drug therapy on humans (more specifically, women).
Some of the MeSH terms were given subheadings (e.g. the term Midwifery was given the
subheading /mt for “methods”.
Written by Seona Hamilton. Please contact your local library or subject librarian for training in literature searching and using
online databases.
Last updated June 2011
2
4 of the terms were “starred” (*) to show that these terms were regarded as showing the main
subject or “focus” of the article.
Why use subject headings?
Some advantages of searching using subject headings rather than free text are:
1. That you tend to retrieve articles that are more relevant:
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Searching using the subject heading Pregnancy will retrieve articles that someone has
decided are about pregnancy.
Searching using the word “pregnancy” will retrieve any article which has the word in the
title or abstract, whether that is relevant to the subject of the article or not (for example, a
brief mention that a particular drug should not be used in pregnancy).
2. That you are more likely to retrieve all instances of a subject, no matter what terms are
used:
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Searching using the subject heading Child will retrieve all* articles where the patient was
a child – if you searched using the word “child” you might miss articles where they
referred to “an eight year old girl” and didn’t use the word child.
*Subject headings are not infallible – to make sure you retrieve ALL relevant articles a
combination of subject headings and free text is often required.
The “Tree” structure of subject headings
Subject headings are usually arranged in a hierarchy of general and more specific terms. This is
often referred to as the “tree” as the more specific terms can be likened to the branches coming
off a general trunk.
e.g. The branches of the general subject heading Pregnancy include:
Pregnancy
Gravidity
Labour, Obstetric
Cervical Ripening
Labour, Onset
Labour Stage, First
Labour Stage, Second
Labour Stage, Third
Trial of Labour
Uterine Contraction
Labour Presentation
Breech Presentation
Maternal Age
i.e Labour Stage, First is more specific than Labour, Onset, which is more specific than
Labour, Obstetric and that in turn is more specific than Pregnancy.
Written by Seona Hamilton. Please contact your local library or subject librarian for training in literature searching and using
online databases.
Last updated June 2011
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(In turn, Pregnancy is a subset of Reproduction, which is a subset of Reproductive and
Urinary Physiology, which is a subset of Biological Sciences)
Searching using subject headings on the OvidSP databases
Subject headings are used only in ‘Advanced Ovid Search’ (‘Basic Search’ requires only a freetext sentence or question, such as the terms you would use in an internet search engine).
Once you have split your question into topics you can try to find relevant subject headings for
these topics.
For example, if your question was about the risks of using tocolytics to stop preterm labour your
topics would be:
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Risk
Tocolytics
Preterm Labour
Type in your search term here and
click on Search
Because the “Map term to subject
heading” box is ticked, the database
will try to suggest suitable subject
headings to match your search topic.
In your chosen database, in this case Medline, enter your topic in the search box and click on
Search.
You can click on the Scope Note
button to get more information about a
subject heading and what it’s used for.
Click on a subject heading to see
where it appears in the “tree”
The database will return a list of possible subject headings. Use your judgement as to which one
seems the most relevant (if any). Sometimes all the subject headings are too specific or too
broad and you will have to conduct a free text search instead.
Sometimes there will be no subject headings that match your term and (after checking your
spelling!) you will have to search using free text for that topic.
Written by Seona Hamilton. Please contact your local library or subject librarian for training in literature searching and using
online databases.
Last updated June 2011
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The next step is to click on the subject heading to see where it lies in the “tree”. This can help to
see whether another more specific subject heading (or a broader one) is available. In this case
we will click on Risk Factors
A “+” sign beside a subject
heading shows that there are
more specific terms available.
Click on the symbol to expand the
tree and see the more specific
terms.
Scroll down the page until you can see your chosen term (highlighted in blue)
You can see here that the subject heading “Risk Factors” is a subset of “Risk”. The broader term
is relevant to the topic but we also are interested in the more specific terms “Risk Assessment”
and “Risk Factors”. To select “Risk” AND all the more specific terms we choose to EXPLODE the
subject heading “Risk” by selecting it and also putting a tick in the first column beside it (which is
marked explode and the top of the page)
By ticking Risk and also the
Explode column we also
automatically select the more
specific terms
Put a tick in this column to
EXPLODE your chosen term.
Scroll back to the top of the page and click on Continue.
The results of the search for
your first term are now
displayed in the Search History
box (click blue area to expand).
Put in your next term and click
Search to find a suitable subject
heading.
A search for a subject heading for Tocolytics brings up only one term: Tocolytic Agents, however
a look at the tree shows more specific terms for individual drug types. Include these in your
search by EXPLODING the term Tocolytic Agents.
Written by Seona Hamilton. Please contact your local library or subject librarian for training in literature searching and using
online databases.
Last updated June 2011
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Always remember to check whether it is worth exploding your terms, otherwise you will miss
potentially relevant articles.
Tick here to include all subheadings.
Click here to continue.
This time, you are asked to choose whether you want to limit your search to particular
subheadings. While subheadings such as Adverse Effects and Toxicity are very relevant to this
particular search, it is worth at this stage always including ALL subheadings. If you get too many
irrelevant results you can always search again by limiting the subheadings you use.
Click on Continue to return to the search page.
Search a third time for subject headings for Preterm Labour in the same way. It matches to the
subject heading Obstetric Labor, Premature which you explode to include the more specific
subject heading, Premature Birth, and include all subheadings.
Now, returning to the search page you can finally join up your three searches by choosing their
tick-boxes and clicking ‘Combine selections with: AND’ so that you limit your search to articles
that are about all three topics.
Scroll down to see the results of your
search, or click the DISPLAY button.
You can now look through the references
and select those that are relevant, or apply
further limits such as publication date and
language.
You can combine subject heading searches with free text searches to broaden your search and
ensure that you haven’t missed any relevant articles because they have been indexed using
different subject headings.
Alternatively, if you have too many articles and are having difficulty finding the relevant ones, you
can search again choosing subheadings to narrow your search terms, or use FOCUS.
Written by Seona Hamilton. Please contact your local library or subject librarian for training in literature searching and using
online databases.
Last updated June 2011
6
Choosing subject headings that are the FOCUS of an article
As mentioned above, indexers will often choose a few subject headings that they regard to be
the main focus of the article.
Choosing to include only those articles where your subject heading(s) are deemed to by the
focus will give you far fewer articles but they should be much more likely to be relevant.
Be aware that by doing this you increase the likelihood that you will miss some articles that may
also be relevant – because of this you should usually not automatically use the focus option
when you start your search. It is however a good way to get a few very relevant references
quickly, or narrow down a very broad search topic.
Click here to
select FOCUS
To choose focus, click in the Focus column on the page where you choose your subject heading,
or click in the second column on the tree page.
IMPORTANT NOTE: Choosing to focus your search does not affect whether you should also
choose to explode a term. You can, and should where relevant, do both. If you choose to focus
an exploded term all the more specific terms will also be focused.
For more information:
Some online tutorials about searching using controlled vocabularies:
MeSH
Pubmed tutorial from the NLM
http://www.nlm.nih.gov/bsd/pubmed_tutorial/m1011.html
OVID Advanced Search overview
http://www.ovid.com/site/help/tutorials_ovidsp_3/advSearch20100429/advSearch20100429.htm
Written by Seona Hamilton. Please contact your local library or subject librarian for training in literature searching and using
online databases.
Last updated June 2011
7