Literature searching for systematic reviews

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Systematic reviews

• “A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question” (Cochrane Library)

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Cochrane Library (2013). About Cochrane Systematic Reviews and Protocols [online]. Available at: http://www.thecochranelibrary.com/view/0/AboutCochraneSystematicReviews.html [accessed 19/7/2013].

Publication bias

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To avoid publication bias the search must pick up on:• All published research:

• In major peer reviewed journals• In lesser known publications

• Any non-published research• Non-English language materials

Finding Published research

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Searching for published research is the easy bit …• Major bibliographic databases e.g. Medline and

Embase• Specialised databases e.g. PsycINFO for

psychology and psychiatry• Trials registers• Hand checking reference lists of relevant

articles• Citation searching – searching for articles that

have cited relevant papers

Finding unpublished research

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Finding unpublished research is not so easy, but there are some good places to start • Trials registers – to identify trials currently in

progress• Conference proceedings• Dissertations• Contacting authors / experts• Searching the websites or repositories of

professional societies, relevant organisations and academic institutions

Resources

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The University of York Centre for Reviews and Dissemination provide a guide to useful resources for systematic review searches

http://www.york.ac.uk/inst/crd/pdf/Finding_studies_for_systematic_reviews.pdf

Search strategies

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• The search needs to be highly sensitive to ensure nothing is missed

• It’s better to be too broad and exclude studies later than miss out on something relevant

• The search strategy needs to be documented

Search strategies

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• Use PICO to break down your search strategy into concepts:

• Patient / population• Intervention• Comparison• Outcome

• You don’t need to use all parts of the PICO if it might restrict your search

Search strategies

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• Identify all possible terms• Think about synonyms, abbreviations,

acronyms, spelling variants• Use both free text searching and

controlled vocabularies (e.g. MeSH)• Look at how relevant papers have been

indexed to identify terms• Look at search strategies of relevant

papers to identify keywords

Search strategies

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• Use operators to combine your searches:• OR to combine related terms, synonyms

etc.• AND to combine all your concepts

together• ADJ or NEAR for terms in close proximity

• Search filters can be used in some databases to identify particular types of study e.g. randomised controlled trials www.york.ac.uk/inst/crd/intertasc/

Summary

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When carrying out a literature search for a systematic review you must:• Search all relevant databases and

other resources• Find unpublished material• Consider all possible terminology• Ensure that your search is broad,

systematic and comprehensive

Further reading

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Both Cochrane and the CRD at York produce comprehensive guides to conducting systematic reviews• http://www.york.ac.uk/inst/crd/SysRev/

!SSL!/WebHelp/SysRev3.htm• http://handbook.cochrane.org/