Searching for Trials for a Systematic Review


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Describe the major available electronic resources
Describe how to build a search strategy
Describe some alternate sources for finding trials
Describe what to do once you get your search results

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  • When creating a complex search strategy as done by a Trials Search Co-ordinator (TSC) or medical librarian, the following is used (similar to when formulating a clinical question). TSCs tend to use population, intervention(s) and condition in their searches but not specific outcomes as this might lead to the search being too narrow. In CENTRAL you do not need to use any terminology for trials as it is made up mainly of RCTs and CCTs. However, RCT filters can be obtained from your Review Group for searching MEDLINE and EMBASE.
  • Here is the completed strategy, using both MeSH and text words. Please note that truncation has been used on the text words ie macula* with and without the r. Text words are in lower caps, MeSH in upper caps. We have put in lines to split the condition and interventions. Explain that it was decided to leave out the population as well as names for other treatments. Joyce – you can now run the search in CENTRAL.
  • The Science Citation Index provides access to current and retrospective bibliographic information, author abstracts, and cited references. Amongst other things you can do cited reference searching on it.
  • Manual searching includes handsearching, whereby you identify a journal in your field of interest and you literally search from cover to cover. Conference proceedings are also a good source of finding trials that may never make it to journal publication. (May want to mention Roberta Scherer’s study regarding ARVO abstracts and how many trials in abstract form never made it to publication in a journal). A good reference point is also the bibliographies of included studies, or other reviews on the subject.
  • Searching for Trials for a Systematic Review

    1. 1. Searching for Trials for a Systematic Review US Cochrane Eyes and Vision Group Completing a Cochrane Systematic Review Workshop July 18, 2013
    2. 2.  Describe the major available electronic resources  Describe how to build a search strategy  Describe some alternate sources for finding trials  Describe what to do once you get your search results Objectives
    3. 3. OK, I Have a Title- What next?  If you are doing a Cochrane review, work with the Trials Search Coordinator for the relevant Cochrane review group.  Work with an information specialist trained in searching for systematic reviews  Use Chapter 6 in the Cochrane Handbook as a guide  Include the search protocol in your protocol (strategy and sources)  Document everything you do and when you do it!!!!
    4. 4. Identification of evidence Develop your protocol for conducting the search:  What sources • Databases • Hand searching  How – search strategies  How to make decisions (duplicate screening?)  How to document – dates, numbers included, excluded
    5. 5.  Cochrane Central Register of Controlled Trials (CENTRAL) (  Includes about 650,000 citations  Includes MEDLINE and EMBASE searches  Includes Cochrane group specialized registers MEDLINE/PubMED (  Includes 22 million citations; > 5,600 journals in 39 languages  Citations fully indexed from 1966 forward  PubMed has most recent – but non-indexed articles  EMBASE (  Includes 25 million citations > 7,600 journals  Includes MEDLINE  Includes > 6 million conference abstracts Major electronic databases used to search for clinical trials
    6. 6. Other important databases  National and regional databases (often local language)  LILACS (  Subject-specific databases  CINAHL (  PsycINFO (  OTSeeker (  Citation databases  Web of Science (  Scopus (  Dissertations, thesis databases  ProQuest (  Grey literature databases  Opengrey ( – formerly SIGLE
    7. 7.  Will review be limited to RCTs or will it include other study designs?  Will adverse events be included?  Is there any geographic consideration?  Is there a limited time period when the intervention was used? Other issues to consider
    8. 8. Add to search strategy  Plurals - (acuity, acuities)  Abbreviations - (e.g., CNV for choroidal neovascularization)  Synonyms -  Lucentis, ranibiuzumab  Avastin, bevacizumab  Spelling variations - (randomized/randomised)  Truncation – (antibod* for antibody or antibodies)
    9. 9.  Medical Subject Headings (MeSH) - Descriptors (with thesaurus) - Most specific term used  Textword searching - titles for all records, abstracts since 1975 - truncation useful  Publication type  Sensitivity (recall) vs Specificity (precision) - no gold standard available Searching trials on PubMed
    10. 10. 1. Start with simple search strategy 2. Run search and retrieve reports 3. Analyze MeSH and text words of studies fitting your criteria 4. Re-run search with revised strategy 5. Repeat steps 2 – 4 if necessary 6. Run optimal search strategy 7. Retrieve reports identified with optimal search strategy Development of MEDLINE search strategy
    11. 11. To develop simple search strategy, start with your question  Population  Intervention(s)  Comparison(s)  Outcome
    12. 12. P I C O For patients with choroidal neovascularization associated with age-related macular degeneration, do intravitreal injections of Lucentis, when compared with Avastin, prevent vision loss? Individuals with choroidal neovascularization associated with age-related macular degeneration Lucentis, ranibizumab Avastin, bevacizumab Change in visual acuity or visual field
    13. 13. Searching PubMED Start with the general format: (Population OR synonym# 1 OR synonym #2) AND (Intervention OR synonym # 1 OR synonym#2) AND (Comparator OR synonym#1 OR synonym#2) AND (Outcome OR synonym# 1 OR synonym # 2) AND Add study type filter terms
    14. 14. How do we find the terms to use in the search strategy?
    15. 15. macular degeneration AND lucentis AND avastin
    16. 16. Text wordsText words
    17. 17. Use the MH – MeSH terms in known articles to build your search strategy
    18. 18. Angiogenesis Inhibitors/ Administra- tion & dosage/ Antibodies Monoclonal/ Administra- tion & dosage Choroidal neovascularization /drug therapy Macular degeneration/ complications/ drug therapy/ physiotherapy Visual acuity/ physiology Visual fields/ drug effects CATT X X Paper 2 X X X Paper 3 X Paper 4 X x X X Paper 5 X X MeSH Analysis
    19. 19. Completed search strategy (this is added to the Cochrane “highly sensitive search strategy”) #1 exp macular degeneration/ #2 exp retinal degeneration/ #3 exp retinal neovascularization/ #4 exp choroidal neovascularization/ #5 exp macula lutea/ #6 maculopath$.tw. #7 ((macul$ or retina$ or choroid$*) adj3 degener$).tw.) #8 ((macul$ or retina$ or choroid$*) adj3 neovasc$).tw.) #9 ((macula$ adj2 #10 or/1-9 #11 exp angiogenesis inhibitors/ #12 exp angiogenesis inducing agents/ #13 exp vascular endothelial growth factors/ #14 (lucentis$ or avastin$ or ranibizumab$ or bevacizumab$).tw #15 (anti adj2 VEGF$).tw. #16 (endothelial adj2 growth adj2 factor$).tw. #17 or/ 11-16 #18 10 AND 17 P I, C Add study filter terms to identify study type
    20. 20. Common errors in search strategies  Spelling errors  Missed spelling variant (randomized instead of random)  Truncation error (methods* instead of method*)  Logical operator error (using NOT instead of AND)  Wrong line number (when combining lines)  MeSH and free text terms on same line  Irrelevant MeSH term  Missed MeSH term  Unwarranted explosion of MeSH terms  Redundancy without rationale  Search strategy not tailored for other databases Sampson et al, J Clin Epi 2006
    21. 21. Use of all databases may be necessary to identify all reports Lawrence et al Inj Prev 2008
    22. 22.  Registers of ongoing or completed trials (WHO portal) Clinical Trial registers
    23. 23. Google Scholar vs PubMed Search engine No citations Mean (SD) Median (IQR) Google scholar 2211 (3999) 1040 (339,1958) PubMed 44 (47) 35 (20,53)  Identified 22 Drug Information Rounds review articles  Searched PubMed or Google Scholar with 2 keywords (MeSH) or text Google presented “older” literature first compared with PubMed - Freeman et al Pharmacotherapy 2009 Similar results reported using clinical query (PubMed) and advanced scholar search (Google scholar) - Anders et al (Resp. Care 2010)
    24. 24.  Journals in topic area  Conference proceedings in area  Bibliographies of related systematic reviews  More efficient and more accurate to use SCOPUS to download all references in a review than to review them manually - Chapman et al, Health Information and Libraries J 2010) Handsearching
    25. 25. Other sources of trial results  FDA  Pharmaceutical company registers  Communication with experts in the field 
    26. 26. Systematic Snowballing Use included articles as a source to identify missing studies:  Reference lists - check cited articles = backward searching  Web of Science, SCOPUS - check citing articles = forward searching  (“Related articles”/ “Find Similar”) in MEDLINE, EMBASE) – also could use to find new terms to expand your search strategy
    27. 27. Use of all sources may be necessary to identify all reports Sources of studies for a systematic review for studies promoting a shift from use of cars to walking or cycling Source Total No. No. in review % Health databases 4 3 14 Citation databases 8 3 14 Other databases 8 2 9 Transport database 33 9 41 Internet search 10 3 14 Handsearch abstracts 6 2 9 Total 69 22 100 Ogilvie et al JECH 2005
    28. 28. Screening search results  Full record citations downloaded from electronic databases into an electronic file – either a text file or a reference manager file  Files distributed to two team members for screening  Yes, Maybe, No  Systematic reviews - obtain full copy for review of references  Disagreements resolved by consensus or by third team member  Electronic documentation  Reference manager – use new field to enter yes/no/maybe/ref  Word – identify using highlighted text, comment box, copy/paste to new file  Excel – possible, but difficult to manage
    29. 29. Screening full text articles  Develop and use a data collection form (paper or electronic)  Query inclusion/exclusion criteria  Duplicate screening - Yes, no, unclear  Disagreements resolved by consensus or by third team member  Responses for excluded studies provide “reason for exclusion” in RevMan  Articles with unclear designation usually need author contact –go into “awaiting assessment” in RevMan  Start to identify multiple articles from same trial  Authors  Numbers of randomized participants  Interventions
    30. 30. Document your findings  When you searched (month/year)  Where you searched  Electronic databases  Handsearches  Trial registers  Communications with experts, industry  Bibliographies, etc.  Internet  How you searched  Search strategies  What you found  PRISMA flow diagram
    31. 31. PRISMA Flow of Information No. records identified through database searching No. additional records identified through other sources No. records screened No. studies included in qualitative synthesis No. full-length articles assessed for eligibility No. records after duplicates removed No. records excluded No. full-length articles excluded, with reasons No. studies included in quantitative synthesis
    32. 32. Conclusions  Develop a search strategy for electronic database searching using an iterative approach, starting with your question  Make sure to perform searches from all additional sources (adapting strategy as necessary)  Document when, where, and how you searched and what you found
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