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What the intervention is to be compared to: eg another intervention, placebo
eg longevity of restorations, pain reduction, quality of life
Example research question
Chlorhexidine for the management of childhood caries
Participants: Children with caries Intervention: Chlorhexidine Comparison: Placebo/no treatment Outcome: management of caries (fewer restorations for example)
For the search…
Take the first two elements of the research question:
List as many synonyms for each as you can
Cochrane systematic reviews aim for MAXIMUM SENSITIVITY, to pick up ALL relevant RCTs
Why not… ?
Why not comparison?
Only in certain circumstances: eg one treatment versus another
Not necessary if placebo or no treatment
Why not outcomes?
Entering outcomes in your search will limit it to studies containing only those outcomes
These may not be in the abstract, and you may risk limiting the search as a result
Task 1 (10 mins)
Use a research question of your own, or use an example research question below to develop a search strategy. List the participants and intervention and find as many synonyms as you can for each term. Use the internet to help you, and try and find an article on the topic that might give you additional keywords.
Example Research Questions:
Alendronate for preventing tooth loss in postmenopausal women
Hypnosis for anxious children undergoing dental treatment
Occlusal adjustment for treating and preventing temporomandibular joint disorders in adults
2. Constructing a search
Cochrane searches are a combination of controlled vocabulary and key words
Controlled vocabulary – what it is and where to find it.
Key word or free text searching
Truncation and proximity operators
Putting it all together
Some databases use subject headings that are arranged in a hierarchy, or tree allowing articles to be collected, labelled and searched using the heading
Subject headings are assigned according to the subject of an article by experienced indexers
The National Library of Medicine in the US has developed an indexing system: Medical Subject Headings (MeSH)
Broader concepts come near the top of the tree, more specific terms lower down
Example of a MeSH Tree
How do I find the MeSH for my topic? Go to: http://www.nlm.nih.gov/mesh/MBrowser.html
To explode or not to explode?
MeSH can be “exploded” to include all the terms that are included in that subject heading on the tree
eg exploding the term “Dental Caries” will make your search include “Dental Caries”, “Dental Fissures” and “Root Caries”
If you want to focus your search to just dental caries without including the terms dental fissures and root caries, use the specific unexploded term “Dental Caries”
Free-text or keyword searching (1)
Searching for MeSH terms limits the search to only include those terms in the subject heading field of a record
Free-text or keyword searching can be applied anywhere in the record – title, abstract, author, keywords or even full-text
You can add a single word, or a phrase: for example: “dental caries”
Free-text searching (2)
Can I just search using free-text and ignore MeSH? Remember: if you just use free-text, the search will be limited to just the phrases you have entered
For example: a search for “maxillofacial abnormalities” as free-text will only pick up records with this phrase
The same phrase exploded in MeSH will also pick up these articles, but also the articles containing subordinate terms on the MeSH tree (example: cherubism, jaw abnormalities)
Boolean operators (1)
Most freetext searches in databases work using Boolean operators:
AND, OR, NOT
AND is used when the article must contain both search terms
OR is used when a paper may contain either search term
NOT is used when the search should retrieve the first term and not the second
Boolean Operators (2) dental floss The AND operator: dental floss AND toothbrushing toothbrushing
Boolean Operators (3) The OR operator: dental floss OR toothbrushing dental floss toothbrushing
Boolean Operators (4) The NOT operator: dental floss NOT toothbrushing dental floss toothbrushing
Boolean Operators (5)
“ dental caries ” AND chlorhexidine will retrieve all articles containing these two terms when they appear together
“ dental caries ” OR “ tooth decay ” will retrieve all articles containing these two terms regardless of whether they appear together or not
AND will REDUCE the number of hits in your search
OR will INCREASE the number of hits in your search
Boolean Operators (6)
“ Cancer NOT children ” is designed to retrieve those articles about cancer but not cancer in children
NOT should be used with caution
Boolean Operators (7)
For example, if the opening sentence of the abstract is:
“ This article looks at cancer but exclusively cancer in adults and not cancer in children”
The search “cancer NOT children” will not pick up this potentially relevant paper, as you have asked the database to search for cancer but not children, and both of these terms are in the opening sentence of the abstract
Boolean Operators (8)
Boolean operators can be used together with brackets
For example: ( tooth OR teeth ) AND caries
This search will retrieve all articles containing the terms tooth and caries, and teeth and caries
Databases can support truncation or enable you to search for the stem of a word e.g.
child * will retrieve child , or children or child’s
Some databases also support wildcard searches e.g.
wom ? n will retrieve women or woman
Symbol for truncation / wildcard can vary
* or $ or ?
Use the help pages of databases to check symbol
Proximity Operators (1)
Some databases allow you to search terms that are in close proximity to each other
This is a more precise way of searching than just using AND
For example, in the Cochrane Library, you can use the operator NEAR
Proximity Operators (2)
“ dental near/6 anxiety”
will retrieve any references where the term dental appears within 6 words of the term anxiety
Not all databases support proximity searching
Operator used in different databases can vary
e.g. in OVID databases, you use “ adj ” (adjacent to) instead of “ near ”
Use help pages of any electronic databases to find out if search method is supported
Putting it all together: p articipants
Synonyms for Dental Caries
Putting it all together: intervention
Synonyms for Chlorhexidine
Putting it all together: adding more (1)
Synonyms for children
child / children
baby / babies
under 5(s) / under 10(s) / under 16(s)
More information needed to decide which to use
Adding more (2) – with caution!
Searching for participant information can be difficult e.g.
if you are looking for adults rather than children, putting the term “adults” in will not necessarily help as “adult” might not be in all the articles you want to retrieve (could be “patients” or “participants”)
Search terms for participants should therefore be used with caution!
Most helpful when there are specific groups
PubMed has search limits that can be added and tested as part of the search
Next steps: MeSH
Take identified synonyms for the participants and intervention
Check whether any of them have a Medical Subject Heading by going to http://www.nlm.nih.gov/mesh/MBrowser.html
Are there any other synonyms in the MeSH tree that could be useful that you can add to your search?
Next steps: free-text
Look at your identified synonyms
Can any of them be truncated?
Are there any alternative spellings?
Participants: Dental Caries
MeSH terms available :
Tooth demineralization (exploded)
First part of PubMed strategy using MeSH:
#1 Tooth demineralization [mh:exp]
[mh] is the way to indicate to PubMed that you are looking for a MeSH term
exp is the way to indicate that the term should be exploded
Participants: Dental Caries
Now begin to build the free-text search:
#2 (teeth AND (cavit* or caries or carious or decay* or lesion* or deminerali* or reminerali*))
#3 (tooth AND (cavit* or caries or carious or decay* or lesion* or deminerali* or reminerali*))
#4 (dental AND (cavit* or caries or carious or decay* or lesion* or deminerali* or reminerali*))
#5 (dentin AND (cavit* or caries or carious or decay* or lesion* or deminerali* or reminerali*))
#6 (enamel AND (cavit* or caries or carious or decay* or lesion* or deminerali* or reminerali*))
#7 (root* AND (cavit* or caries or carious or decay* or lesion or deminerali* or reminerali*))
Participants: Dental Caries
Once all the MeSH and free-text terms have been added, you need to tell the database to search for all the terms together
Line 8 should read:
#1 or #2 or #3 or #4 or #5 or #6 or #7
This tells PubMed to retrieve all of these search terms
Now the search for the participants is complete, Line 9 of your search should move to the intervention
Using the same process, find appropriate MeSH and build a free-text search
#9 Chlorhexidine [mh:noexp]
#10 (chlorhexidine or chlorohex* or eludril* or corsodyl* or PerioChip*)
#11 (“mk 412a” or mk412a)
#12 (nolvasan* or sebidin* or tubulicid* or cervitec* or chlorzoin*)
#13 chx [tiab]
#14 #9 or #10 or #11 or #12 or #13
A word about line 13:
#13 chx [tiab]
Initials should be used in a search with caution: although unlikely in this case, your search could potentially pick up an author’s initials: eg C.H.X. Smith
The search here has been limited to just the title and abstract: [tiab] so that the author field is not searched
Condition and intervention
The final line of your strategy should bring the participants and intervention together by using the AND command
In this case: #8 AND #14
This means that all the terms you have entered are included in the search, but only those articles which include the terms for the intervention PLUS the terms for the participants will be retrieved
3. Testing the strategy
The next step is to have a test run of the strategy in PubMed Advanced Search
Is the number of hits manageable?
Are any lines retrieving no hits?
Have you spelled everything correctly?
Have you truncated everything correctly?
Check the keywords that relevant articles have been indexed with: can any of them be added to the search?
Try out the search limits: are these helpful?
Task 2 (20 mins)
1. Find the MeSH terms for your chosen topic.
Go to the National Library of Medicine MeSH browser: http://www.nlm.nih.gov/mesh/MBrowser.html
Enter the search terms and synonyms and make a note of the MeSH terms for your topic. Do any need to be exploded?
2. Look at your identified synonyms and think about how to build a free-text search:
Can any of the terms be truncated? Are there any alternative spellings? (for example, think about US English v British English spelling: -ize versus -ise or -ization versus -isation.) Are there any terms that can be represented by initials alone? How should these be represented in the search?
3. Now test your search in PubMed (use Advanced Search)
4. What are search filters?
There are standardised methodological search filters available if you are searching for a particular kind of study
the Cochrane Collaboration has developed a filter to retrieve randomized controlled trials and controlled clinical trials
Search filters can be added to your search to make them more precise
There are search limits in PubMed, but the Cochrane filter has been rigorously tested against a gold standard
Cochrane Highly Sensitive Search Strategy for identifying randomized controlled trials in MEDLINE:
#1 randomized controlled trial [pt]
#2 controlled clinical trial [pt]
#3 randomized [tiab]
#4 placebo [tiab]
#5 drug therapy [sh]
#6 randomly [tiab]
#7 trial [tiab]
#8 groups [tiab]
#9 #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8
#10 animals [mh] NOT humans [mh]
#11 #9 NOT #10
Reference: The Cochrane Handbook for Systematic Reviews of Interventions, Version 5.1.0, [updated March 2011], box 6.4a
Adding a search filter
To add a search filter to your search to make the search more precise:
Enter your subject search (participants/interventions) into PubMed
Enter the search filter, exactly as written
Add an “ AND ” command line to link the last line of the search filter with the last line of the subject search
Other search filters are available for
The InterTASC website has examples of all of these and more, plus information on how they were developed and tested:
Task 3: Adding a Filter (10 mins)
Add a methodological search filter to the search you built in Task 2.
Check your worksheet for the Cochrane Highly Sensitive Search Strategy for identifying RCTs in PubMed and enter the terms
Join the subject search from Task 2 and the Filter by using the “AND” command
Translating the strategy
Once you are happy with the PubMed strategy, you need to translate it for other databases you intend to search
Check the database help pages / try running the strategy to make sure that you are using:
the correct symbols to truncate
the correct search terminology
(eg is there a different way of searching for title/abstract keywords?)
the correct MeSH terms
If a line of your search retrieves less hits than expected, you may have to change it
Task 4: Translating the strategy (10 mins)
Translate your search for use in the Cochrane Library.
Go to http://www.cochrane.org and click on the “Cochrane Library” (top right)
Click Advanced Search
Check the tips on your worksheet and translate your PubMed Search to the correct search syntax for the Cochrane Library
5. Do I need to handsearch as well?
Handsearching requires the searcher to read/scan a journal page by page to identify relevant studies, including abstracts and correspondence
A Cochrane Systematic review has demonstrated that handsearching in addition to electronic searching is the best technique for retrieving all relevant studies
Hopewell S, Clarke MJ, Lefebvre C, Scherer RW. Handsearching versus electronic searching to identify reports of randomized trials. Cochrane Database of Systematic Reviews 2007, Issue 2. Art. No.: MR000001. DOI: 10.1002/14651858.MR000001.pub2.
Why do handsearching? Isn’t electronic searching enough?
Electronic searching will only pick up records in which the subject and study design information is given in either the title, abstract or keywords assigned to the paper
Many citations do not have abstracts – leaving only the title - publication type - and keywords to be searched electronically
The Cochrane Collaboration runs a handsearching programme to identify randomized and controlled clinical trials in the literature
These are then added to the Cochrane Library
Before handsearching, check with your Trials Search Co-ordinator which journals have already been searched – it may not be necessary
Documenting your search
Writing up the search is an important part of doing a systematic review
All search strategies should be included in your review AS RUN in the database – the idea being that another researcher could easily replicate them
For Cochrane Reviews, all search strategies should be put in appendices along with search filters and number of references retrieved
Contact for help with any aspect of literature searching for a Cochrane systematic review:
Anne Littlewood, Trials Search Co-ordinator, Cochrane Oral Health Group