searching workshop new york 2011
TRANSCRIPT
Searching for Studies
Anne Littlewood Sue FurnessTrials Search Co-ordinator Editor/Methodological Support
Cochrane CollaborationOral Health Group
University of Manchester, UK
1. Which databases should I search?
2. How do I construct a search?
3. How do I test the strategy?
4. What are search filters?
5. Do I need to do handsearching as well?
Searching for evidence…
http://www.flickr.com/photos/jakebouma/3345296623/
Why is a good search strategy important?
• Ensures that a variety of sources of information are included
• Makes sure that all relevant studies are identified
• Reduces the risk of bias
• Ensures that others can replicate your study
1. Which database?
• Selection of databases is very important and depends on topic
• MEDLINE should always be used for medical / dental searches
• EMBASE is an alternative
• CENTRAL at the Cochrane Library should be searched for systematic reviews or studies involving controlled trials (RCTs/CCTs)
Other sources
• CINAHL: for topics involving nursing or care
• PsycINFO: for topics involving psychology (eg Dental Anxiety)
• LILACs: database of health care in Latin America – useful for non-English language references
• Cochrane Specialized Registers: OHG Register has over 26,000 citations (RCTS, CCTs and systematic reviews)
Grey Literature
• Grey literature: that which cannot be obtained readily from normal book/journal channels
• Sources: – OpenGrey - open access to 700,000 bibliographical references of
grey literature (paper) produced in Europe and allows you to export records and locate the documents
– Web of Knowledge: allows searching of Conference Proceedings
– ClinicalTrials.gov: access to ongoing trials in the USA
– Meta Register of Controlled Clinical Trials (mRCT): www.controlled-trials.com
Which platform?
• Databases are often available from more than one source, e.g.– MEDLINE is available via:
• OVID• PubMed• EBSCO • Silverplatter• Etc...
• Make sure you check which are available to you from your librarian
Remember…
• A search designed for one database or platform will not work in another! – For example, a search designed to be used in PubMed will not
work in the Cochrane Library
• A search designed to work in MEDLINE via PubMed will not work in MEDLINE via EBSCO– For each database/platform, check the help pages to see how
you should conduct your search
• See your librarian / Trials Search Co-ordinator for advice!
Building a Strategy
A well constructed research question is the place to start
Research Questions
• A medical research question could contain four elements that can be broken down as:
•Participants eg children with caries, smokers with periodontal disease
•Intervention eg antibiotics, physiotherapy, powered toothbrushes
•Comparison What the intervention is to be compared to: eg another intervention, placebo
•Outcomes 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:
1. Participants2. Interventions
• 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
• Boolean operators
• Truncation and proximity operators
• Putting it all together
Controlled Vocabulary
•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
• Stomatognathic Diseases
• Tooth Diseases
• Tooth Demineralization
• Dental Caries
• Dental Fissures
• Root Caries
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
TruncationDatabases can support truncation or enable you to
search for the stem of a word e.g.
• PubMed:– 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: participantsSynonyms for Dental Caries
– Tooth/teeth decay– Tooth/teeth demineralization– Tooth/teeth remineralization– Tooth/teeth cavities– Tooth/teeth lesions– Enamel/dentin decay– Root caries
Putting it all together: interventionSynonyms for Chlorhexidine
– Chlorohex– Eludril– Corsodyl– PerioChip– CHX– MK-412a– Nolvasan– Sebidin– Tubulicid – Cervitec– Chlorzoin
Putting it all together: adding more (1)Synonyms for children
Possibilities:– infant(s)– toddler(s)– child / children– baby / babies– pre-school child(ren)– adolescent(s)– teenager(s)– 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
Intervention: Chlorhexidine
• 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
Intervention: chlorhexidine
• #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
Intervention: chlorhexidine
• 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)
http://www.ncbi.nlm.nih.gov/pubmed
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
Search filters
• Other search filters are available for– Systematic Reviews– Observational studies– Outcome studies– Therapy studies– Diagnostic studies
• The InterTASC website has examples of all of these and more, plus information on how they were developed and tested:
• http://www.york.ac.uk/inst/crd/intertasc/
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.
Handsearching (2)
• 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
Handsearching (3)
• 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
Any questions?
Contact for help with any aspect of literature searching for a Cochrane systematic review:
• Anne Littlewood, Trials Search Co-ordinator, Cochrane Oral Health Group– Email: [email protected] Tel: +44 161 275 7814