Medline (Ovid) worked example of a search strategy
Does the MMR vaccine cause autism?
You can return to the main search page at any stage, by clicking the Search tab near the top of the screen.
Step 1: PICO formula
Using the PICO formula, identify what you want to discover.
P (population/problem) = autism (autistic spectrum)
I (intervention) = MMR vaccine
C (comparison) = no MMR vaccine (no need to include this in your search)
O (outcome) = causation (etiology, risks)
Next, identify the main concepts, then list any synonyms or related terms to include in your search
strategy. Think about the appropriate research methodologies for answering this kind of question (see
under Clinical Queries below).
Step 2: Using the subject headings
When you have logged in, make sure that Map Term to Subject Heading is ticked. Type in your search
term autism and click Search. Medline will display one or more subject headings which may be suitable.
Next to each one, you will see a link to a Scope Note
Check the Scope Note to:
o Confirm that the term is appropriate to your research question
o Check the Used For list of synonyms or alternative terms to identify possible free text search terms to
back up the subject heading searches (e.g. autistic, kanner, kanner’s)
o Find any Related Terms to add as separate searches within your search strategy
Click on the Subject Heading Autistic Disorder to view the Tree and to consider functions Explode and
Focus. As no narrower terms are listed under Autistic Disorder, there is no need to explode the term.
Note the related term Asperger Syndrome. Click Continue.
In case there are narrower terms listed below: Select the Explode box of the term and you will get the
selected term in combination with all its narrower, more specific terms.
The Subheading Display shows a list of subheadings which you can use to restrict your search to specific
aspects of this subject, such as diagnosis, and so on. At this stage, include all subheadings, but note any
you may want to use later, if your final set of results is too large. Click Continue. Now run a subject
heading search for MMR.
Step 3: Free-text searches
Run free-text searches, using shortcuts to widen your search. Add .tw. to each search term to tell the
software to look in titles and abstracts. For example: autis*.tw., MMR.tw.
When you have done more than four searches, your earlier searches will start to disappear from the
search history display. You can continue to see them by clicking Expand, next to the search history box.
Step 4: Combine subject heading and free text searches
Use OR to combine all the search sets about the same concept. OR finds any one or more of your selected
terms.
Use AND to combine the search sets about different concepts. AND finds all your selected terms.
Step 5: Expand your search strategy to maximize inclusion of relevant references
Click on Complete Reference within the results list to see additional subject heading and text word terms
to include in your search strategy.
Step 6: Focus results
If your search strategy finds too many results, you can Focus one or more of your MeSH terms to restrict
your results to articles where the subject heading represents a major concept. Search your term again
through the vocabulary and choose Focus or type an asterisk followed by the set number, e.g. *10.
However, this may mean that you lose relevant papers.
You could include causation as concept at this point by choosing the subheading Etiology.
Step 7: Use Clinical Queries
The Clinical Queries limits enable you to restrict your results to articles which use appropriate
methodology for answering different kinds of clinical questions, including etiology. It is usually best to
start by selecting the ‘optimised’ focus. You will find the Clinical Queries limits by selecting Limits from
the main search page, then select Additional Limits.
Step 8: Apply limits and subheadings
If the set of results is still too large, you can use limits to reduce your results in various ways. However,
you do run the risk of removing some relevant papers. Apply one limit at a time and view the results
before adding further limits.
Re-run subject heading searches to include subheadings and restrict to a particular aspect of Autism or
MMR by clicking the box before the subheading f.ex. Adverse effects, which restricts your results to only
those references concerned with adverse effects.
Evaluating the results
1. Have you retrieved too much or not enough results?
 Use more limits or remove limits
2. Are the search results irrelevant to your topic?
 Check your search terms and use another search strategy
3. Repeat your search in other databases if necessary
Based on Medline search strategy guide by University of Bristol
http://www.bris.ac.uk/library/support/subjects/medfac/trainingguides.html
14.9.2011/ma and pn