MEDLINE Searching Using OvidWeb
Searching Ovid MEDLINEŽ
What is MEDLINE?
MEDLINE:
NOT just another Internet search engine
Getting connected to Ovid MEDLINEŽ
Basic
MEDLINE searching
Tricks for refining your search
Combining
sets
AND versus OR
Limiting a search
Viewing
and selecting results
Printing,
emailing, and saving results
Getting the full-text of the article
Author, title, or journal searches
Find similar articles and citing articles
Clinical Queries
Troubleshooting your results
For more help
What is MEDLINE?
MEDLINE is the United States' National
Library of Medicine's premier bibliographic index to the biomedical journal literature.
It covers:
-
all health sciences including medicine, nursing, dentistry,
allied health, and veterinary medicine
-
the pre-clinical sciences such
as biology, biochemistry, genetics, microbiology, physiology, and anatomy
-
related disciplines such as health care administration,
biomedical engineering, clinical nutrition, psychology, and social work.
MEDLINE provides citations and abstracts to
journal articles and other professional publications. It provides coverage
from the 1950s to the present, contains over 16 million records, and indexes
approximately 4800 journals published in the United States and over 70 other countries.
MEDLINE is available at Dana Medical Library through Ovid Technologies, a
commercial vendor.
MEDLINE: Not
just another Internet search engine
MEDLINE, as an electronic database, was created
long before the advent of powerful Internet search engines capable of performing
rapid keyword searches. Although keyword searches can be done in MEDLINE, the main search mechanism is through the use of subject headings (often
referred to simply as "terms"). These can be likened to the terms found in
the back-of-the-book index of a typical textbook that aid the reader in
rapidly locating the page on which a given topic is discussed. Similarly,
the MEDLINE subject headings are used to quickly find any records in the
database on that topic.
Each article indexed in MEDLINE is assigned an
average of 10-12 subject headings, based on its subject content.
The subject headings are assigned by human indexers through manual review of the
article, not by computer algorithm. For any search term entered, the Ovid
software will automatically display a list of possible MEDLINE subject
headings from which to make selections.
Although there is the option to search by keyword
in MEDLINE, searching via the subject headings will usually produce better
results with fewer irrelevant hits. Exceptions to this rule do exist, for
example when searching for proper names, trade names, specialized jargon, and
newly coined terms.
Connecting to Ovid MEDLINEŽ
From Dana Library's home page (http://library.uvm.edu/dana),
click on "OVID" under "Databases & E-Books".
Select the desired segment of Ovid MEDLINEŽ, or choose the entire database,
including "In-Process Citations and other Non-Indexed Citations".
For off-campus access to Ovid MEDLINEŽ, click on the "Connect
From Off Campus" button on the left sidebar of Dana Library's home page for instructions and links.
Basic MEDLINE searching
One of the most crucial steps to performing a successful literature search is
formulating a search question and then identifying the searchable concepts.
Let's suppose you want to find articles
discussing the use of Factor VII in the treatment of intracerebral hemorrhage.
Here the most likely searchable concepts are "Factor VII" and "intracerebral
hemorrhage", although other terms may produce relevant results as well.
Once you have identified the searchable
concepts, search on each one separately rather than as a multiple word
string. When you have created a separate set for each concept, combine the
sets.
Using the above example, begin by connecting
to Ovid MEDLINEŽ. Then...
- For the first concept, enter "Factor
VII" in
the search box, and click Search or simply press the Enter key.
- In the mapping display, check the box next to
the one most appropriate term from the list displayed. In this case
there is only one subject heading displayed, but often there are many more. As explained above, select the keyword option only as
a last resort. For this example, check the box next to "Factor VII".
- Optional step: to view a short definition
(Scope Note) for a particular term, click on the small blue information
icon ("i").
This will identify synonyms, related terms, and the year the term was
introduced into the vocabulary list.
- Any term selected will automatically be
exploded unless you un-check the Auto-Explode box. (See the Explode
section under "Tricks for refining your search".)
- Check the Focus box if desired.
(See the Focus section under "Tricks for refining your search".)
- Click Continue.
- Select one or more
subheadings, or accept the default option to Include All Subheadings.
- Click Continue. You will now be back at the Main Search Page, having generated the
first set of your literature search.
- Now enter the second term, "intracerebral
hemorrhage", and repeat the above steps to generate a second set of results.
Click on the scope note to verify that "Cerebral hemorrhage" is the
appropriate subject heading.
- Read the next section for tips on refining your search, or skip to
Combining Sets.
Tricks for refining your search
MEDLINE provides a number of powerful tools with which to
fine tune your search and eliminate less relevant hits. These can be used
alone or in any combination.
Explode
When you explode a term, you
direct the system to search for that term, plus any more specific terms
associated with it. For example, if you explode the term "Wounds
and Injuries", your search will include all the specific types of wounds such
as burns, contusions, fractures, etc., as well as the more general term.
Alternatively, you
may choose not to explode, prompting the system to search only on the general term but
not the more specific terms.
In order to decide if you want to explode, click on the hyperlinked term in the mapping display to access the
hierarchical list of subject headings. Scroll down
until you encounter the highlighted original term. Note that with each
successive indentation, the terms become progressively more specific.
To explode, check the box in the explode column next to the broader term.
If you explode a term, the result
will be a larger set than if you searched only on the more general term.
Use this feature with caution, as you may or may not want to search on all the
more specific terms.
Continuing
with the above example, you'll note that the term "Cerebral Hemorrhage" has
two more specific terms nested beneath it, "Basal Ganglia Hemorrhage" and "Traumatic Cerebral Hemorrhage". In this case, exploding will probably be helpful.
Similarly, the term "Factor VII" has a narrower term, "Factor VIIa
(activated)", which
you'll probably also want to include in your search strategy.
By default, Ovid MEDLINEŽ will explode any subject heading you select
unless you direct the system otherwise. In the search history display, the
code "exp" will precede any subject heading that was exploded.
Focus
The focus feature will limit your search to articles in which the term is the main
topic, eliminating those with only a very brief or general discussion of the
term. The final result will be a smaller, more "focused" set of
citations, since the less relevant citations will have been excluded.
Using the focus feature is one of the most effective methods for
reducing the total number of hits while simultaneously maintaining or
increasing overall relevancy. The term "Cerebral Hemorrhage" produces a very large number of hits, so it
may be helpful to use the focus feature in this example.
In the search history display, an asterisk will precede any
subject heading that was "focused".
Subheadings
Subheadings allow you to
concentrate your search on one particular aspect of a subject. In our example, since you are primarily interested in
the therapeutic treatment of intracerebral hemorrhage, you could select the "Drug
Therapy" subheading.
Like the focus feature, the use of subheadings
has the effect of producing a smaller total number of hits, while increasing the
overall relevancy of the set. However, you run the risk of accidentally
eliminating some
relevant citations by using subheadings, so use this feature with caution.
Combining sets
After creating a separate
set of results for each concept, combine the sets by clicking on the Combine Searches
button. Select
the sets you wish to combine, and click Continue.
You'll need to decide if
you want to combine the sets using AND or OR. The default is AND.
It's use will result in a smaller set of results, in which each citation will be
listed under both subject headings. Refer to the following section for a
detailed explanation of AND and OR.
AND versus OR
To understand the difference between the
Boolean operators AND and OR, it may help to think of them in terms of making a purchase. Suppose you need to buy a new car,
and
need to make
decisions regarding body type, engine size, and color, among other
characteristics.
Let's say you decide
that you want a silver 4-door sedan with a 6-cylinder engine.
Expressed in Boolean terms, you would say you want a "4-door
sedan AND 6-cylinder engine AND silver". The Boolean operator AND
will generate a relatively small set of cars of which each
will satisfy all the criteria. It will NOT
include any cars that are missing any one of the criteria, even if they have
the other two. Thus, it will not include any cars that are not silver
in color, even if they are 4-door sedans and/or have a 6-cylinder engine.
Conversely, suppose
you are very flexible in your desires and you decide that you would indeed be
perfectly happy with
a car that is either a 4-door sedan OR a 6-cylinder engine OR is
silver in color. Here, the Boolean operator OR will create a relatively large set
of cars, each of which will satisfy at least one of the criteria
but not necessarily all of them. So you may have many 4-door sedans to
choose from, but they may or may not have a 6-cylinder engine and they may or may
not be silver in color.
Many techniques used in database searching are based on the principles of
Boolean logic (or Boolean algebra). For the curious among us, the term "Boolean" comes from George Boole, the
19th century English mathematician who developed this system of
logic. If you'd like to learn more, check out this web page from
Creighton University.
http://www.hsl.creighton.edu/hsl/Searching/Boolean_operations.html
Limiting
Develop your search strategy before applying
limits.
The most commonly used
limits, including Humans, English Language, Core Clinical Journals, and Local
Holdings, are provided just below the search box on the Main Search Page.
The Local Holdings limit will restrict your search to articles in journals subscribed to by
the University of Vermont (UVM).
Additional limit options
can be found by clicking on the More Limits button. These include
limits for age groups, journal subsets, and publication types such as clinical
trials, randomized controlled trials, practice guidelines, meta analysis, or
review articles. Pull the scroll bar down to view the entire screen.
Limit in stepwise fashion
rather than all at once so that you have the option of going back to a larger,
less restricted set if necessary.
Viewing and selecting
citations
Click on the Display
button for the set you wish to view. The citations will be listed in
reverse chronological order (most recent listed first.) The citations will be displayed in the
brief format, which includes citation, publication type, local holdings
message, and unique identifier (UI). The minimum information required
to locate an article is listed in italics and consists of the journal title,
volume, issue, page numbers, and date.
To view the abstract or
the complete reference - which includes the subject headings and additional
database fields, but not the
full-text of the article - click on the appropriate hyperlink. The author name
subject headings will be hyperlinked, enabling you to launch new searches
instantly.
All abstracts and subject
headings will appear in
English even though the article itself may be written in a non-English language.
To check the UVM Libraries Online Catalog for
available issues, click on the Library Holdings link, opening a new browser
window. If UVM has an
electronic subscription to the journal, a URL will be provided which will direct you to the publisher's website. Browse the archive of past issues for the
desired article. Click on Return to Session to resume your Ovid MEDLINEŽ
search.
The Ovid Full Text button links to
electronic journals that UVM subscribes to through Ovid. To view a list of
these journals, go to Dana Library's home page and
click on Electronic Journal Packages under the Electronic Journals heading.
Check the boxes on the
left margin to mark any records you wish to save for printing or
e-mailing. When you are finished browsing the set, click on Main Search
Page. A new set will have been created consisting of the records you
selected.
Printing, emailing, and
saving results
Scroll down to the
Results Manager located at the bottom of the page. Indicate which
citations you want and the desired fields (the default is Citation + Abstract).
Always check Include Search History so that you can repeat your
search at a later date if necessary.
To print the results,
click on Print Preview, followed by your browser's print function.
To e-mail or save the citations, click on the
appropriate button and follow the prompts.
Getting the
full-text of the article
Use the Local Holdings limit to restrict your search to journals subscribed to by UVM,
either electronically or in print.
To check the UVM Libraries Online Catalog
for available issues, click on the Library Holdings link. If UVM has an
electronic subscription to the journal, a URL will be provided that will take
you to the publisher's website. Browse the archive of past issues for the
particular article.
The Ovid Full Text button links to electronic journals that UVM subscribes to
through Ovid. To view a list of journals subscribed to through Ovid, go to
Dana Library's home page, and click on Electronic Journal Packages under the Electronic
Journals heading.
For
off-campus access to UVM electronic journals, refer to the Connect From Off Campus link on the Dana
Library home page.
Journals available in print are shelved
alphabetically by title in the periodical section of Dana Library. Journals dated pre-1985 are housed in the Library Research Annex,
located on Catamount Drive next to UVM Police Services on the east side of East
Avenue. Consult the UVM Libraries Online Catalog for detailed information
about specific journal titles.
Unbound journal issues from the current year
are shelved in the lounge area.
Author, title, or
journal searches
To search for articles written by a specific
author, click on the Author tab above the search box. Enter the author's
last name, a space, and the first letter of the first name. Select all variations of the name, noting that an author may be
listed with only a first initial or with both the first and middle initials.
To search for an article for which you only
know a word or phrase from its title, click on the Title tab, and enter the
word or phrase in the
search box.
To search for all articles in the MEDLINE
database from a given journal, click on the Journal tab. Enter the first
word or two of the full journal title (do not use abbreviations.)
Find similar articles and citing articles
Find Similar and Find Citing Articles permit you to expand a search without ever
having to enter additional terms. They are excellent tools for finding
additional articles when your search is producing too few results or when you need
to perform a highly comprehensive search. Simply click on the appropriate
link in the brief (default), abstract, or complete reference display.
Find Citing Articles connects you to a list of more recent
articles that cite the original article. It is most useful for older
articles, since it takes a number of years before an article will be cited by
new publications. By clicking on Complete Reference for a citing article,
the entire bibliography of the citing article will be displayed, including the
original article.
Clinical Queries
This feature is found by clicking on the More Limits button.
The Clinical Queries feature is intended for use by
clinicians wishing to restrict their searches to clinically sound research
studies. There are nine broad categories of searches available: Therapy,
Diagnosis, Prognosis, Etiology, Reviews, Clinical Prediction Guides, Qualitative
Studies, Costs, and Economics. Each of these search categories may in turn
be designated as sensitive, specific, or optimized. A sensitive search will
bring up most relevant articles but some less relevant ones as well, a
specific search will bring up most of the relevant articles but miss a few of
them, and
an optimized search will attempt to balance sensitivity with specificity.
These filters are based on the work of R. Brian Haynes,
MD, PhD et al. of the Health Information Research Unit at McMaster University.
A detailed explanation of these limits can be found at http://hiru.mcmaster.ca/hedges/.
Troubleshooting
Q. What do I
do if I get too many results?
- add
another search term, using "AND" to make a smaller set
-
substitute a more specific term
- remove
the Explode feature
- add the
Focus feature
- add one
or more subheadings
- place a
limit on the final results (e.g., publication type, age group, publication year,
etc.,)
Q. What do I
do if I get too few results?
-
remove a term if you
combined more than one term with AND
- search on
related terms, using OR to make a larger set
-
substitute a more general term
- add the
Explode feature
- remove
the Focus feature
- remove
subheadings, and instead accept the default of All Subheadings
- remove
limits, broaden them, or apply them incrementally
For more help
If you would like more help with searching Ovid MEDLINEŽ or
any of the other bibliographic databases, please call the
Dana Medical Library Reference Desk at
656-2201, send an email to danaref@uvm.edu,
or send an AOL Instant Message to our screen name "danaref". Or even
(gasp!),
come see us in person. We also offer private tutorials and classes to individuals
and small groups. Call the reference desk for more information.
Frances Delwiche, Reference
Librarian, Dana Medical Library, University of Vermont,
fdelwich@uvm.edu 01/18/06
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