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Information In Practice

Effectiveness and efficiency of search methods in systematic reviews of complex evidence: audit of primary sources

BMJ 2005; 331 doi: (Published 03 November 2005) Cite this as: BMJ 2005;331:1064
  1. Trisha Greenhalgh, professor of primary health care (p.greenhalgh{at},
  2. Richard Peacock, clinical librarian2
  1. 1Department of Primary Care and Population Sciences, University College London Medical School, Holborn Union Building, London N19 5LW
  2. 2Archway Healthcare Library, Holborn Union Building, London
  1. Correspondence to: T Greenhalgh
  • Accepted 14 September 2005


Objective To describe where papers come from in a systematic review of complex evidence.

Method Audit of how the 495 primary sources for the review were originally identified.

Results Only 30% of sources were obtained from the protocol defined at the outset of the study (that is, from the database and hand searches). Fifty one per cent were identified by “snowballing” (such as pursuing references of references), and 24% by personal knowledge or personal contacts.

Conclusion Systematic reviews of complex evidence cannot rely solely on protocol-driven search strategies.


  • Competing interests None declared.

  • Accepted 14 September 2005
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