Incorporating Evidence: Searching for Studies

Anne LittlewoodTrials Search Co-ordinator

Cochrane CollaborationOral Health Group

University of Manchester

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

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 Review Groups and their specialized registers

Grey Literature

• Grey literature: that which cannot be obtained readily from normal book/journal channels

• Sources: – OpenSIGLE (System for Information on Grey Literature in Europe)

– ZETOC: Free search 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 • 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!

Controlled Vocabulary•The National Library of Medicine in the US has developed an indexing system: Medical Subject Headings (MeSH)

•Some databases use subject headings that are arranged in a hierarchy, or tree

•Broader concepts come near the top, more specific terms lower down

•Subject headings are assigned according to the subject of an article by experienced indexers at the National Library of Medicine

•MEDLINE, EMBASE and CINAHL all use MeSH

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 searching (1)

• Searching for MeSH terms limits the search to only include those terms in the keyword 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 databases work using Boolean operators:

AND, OR, NOT

• AND is used when the article must contain both 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)

Cars

The AND operator: cars AND buses

Buses

Boolean Operators (3)

The OR operator: cars OR buses

CarsBuses

Boolean Operators (4)

The NOT operator: cars NOT buses

Cars Buses

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

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, adults, smokers

•Intervention eg antibiotics, physiotherapy, powered toothbrushes, education programme

•Condition eg caries, temporomandibular joint disorders, halitosis

•Outcomes eg longevity of restorations, pain reduction, quality of life

Example research question

• Chlorhexidine for the management of childhood caries

Participants: children

Intervention: chlorhexidine

Condition: caries

Outcome: management of caries (fewer restorations for example)

Next steps

• Take three elements of the research question1. participants2. interventions 3. condition

• List as many synonyms for each as you can

• Why don’t we use outcomes for searching?– Entering outcomes in your search will limit it to studies

containing only those outcomes.

Condition

Synonyms for Dental Caries

– Tooth/teeth decay– Tooth/teeth demineralization– Tooth/teeth remineralization– Tooth/teeth cavities– Tooth/teeth lesions– Enamel/dentin decay– Root caries

Intervention

Synonyms for Chlorhexidine

– Chlorohex– Eludril– Corsodyl– PerioChip– CHX– MK-412a– Nolvasan– Sebidin– Tubulicid – Cervitec– Chlorzoin

Participants (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

Participants (2)

• 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

• Search terms for participants should therefore be used with caution!

Next steps: MeSH

• Take identified synonyms for the condition 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? – Are there any hyphens?

• e.g. “tooth demineralisation” OR “tooth demineralization”

• “mk-412a” OR “mk 412a” OR “mk412a”

Condition: Dental Caries

• MeSH terms available:

• Dental Caries (exploded)

• Tooth Demineralization (not exploded)

Condition: Dental Caries

• First part of PubMed strategy using MeSH:

– #1 Dental Caries [mh:exp]

– #2 Tooth Demineralization [mh:noexp]

• [mh] is the way to indicate to PubMed that you are looking for a MeSH term

Condition: Dental Caries• Now begin to build the free-text search:

– #3 (teeth AND (cavit* or caries or carious or decay* or lesion or deminerali* or reminerali*))

– #4 (tooth AND (cavit* or caries or carious or decay* or lesion or deminerali* or reminerali*))

– #5 (dental AND (cavit* or caries or carious or decay* or lesion or deminerali* or reminerali*))

– #6 (dentin AND (cavit* or caries or carious or decay* or lesion or deminerali* or reminerali*))

– #7 (enamel AND (cavit* or caries or carious or decay* or lesion or deminerali* or reminerali*))

– #8 (root* AND (cavit* or caries or carious or decay* or lesion or deminerali* or reminerali*))

Condition: 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

• Line 9 should read:– #1 or #2 or #3 or #4 or #5 or #6 or #7 or #8

• This tells PubMed to retrieve all of these search terms

Intervention: chlorhexidine

• Now the search for the condition is complete, Line 10 of your search should move to the intervention

• Using the same process, find appropriate MeSH and build a free-text search

Intervention: chlorhexidine

• #10 Chlorhexidine [mh:noexp]

• #11 (chlorhexidine or chlorohex* or eludril* or corsodyl* or PerioChip*)

• #12 (mk-412a or “mk 412a” or mk412a)

• #13 (nolvasan* or sebidin* or tubulicid* or cervitec* or chlorzoin*)

• #14 chx [tiab]

• #15 #10 or #11 or #12 or #13 or #14

Intervention: chlorhexidine

• A word about line 14:

• #14 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 condition and intervention together by using the AND command

• In this case: #9 AND #15

• 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 condition will be retrieved

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?

Search filters

• There are standardised search filters available if you are searching for a particular kind of study e.g.

– the Cochrane Collaboration has developed a filter to isolate randomized controlled trials and controlled clinical trials

– Search filters can be added to your search to make them more precise

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] and animals [mh])• #11 #9 not #10

• Reference: The Cochrane Handbook for Systematic Reviews of Interventions, Version 5.0.1, [updated September 2008], 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 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:

• http://www.york.ac.uk/inst/crd/intertasc/

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

Handsearching (1)

• 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

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

Documenting your search

• In the text of your review

– List the electronic databases you have searched and the dates you have searched from and to

– Reference any search filters you have used

– Comment on any language restrictions

– List the journals you have handsearched

Any questions?

Contact for help:

• Anne Littlewood, Trials Search Co-ordinator, Cochrane Oral Health Group– Email: a.littlewood@manchester.ac.uk Tel: 0161 275 7814

• I can conduct searches for Cochrane systematic reviewers, or advise on any part of your search strategy