This document discusses the importance of including grey literature in medical and clinical research. It notes that traditionally research has relied on published clinical trials but there is now a push to include unpublished trials found in sources like clinical trials registries and conference proceedings. Excluding unpublished trials can introduce bias into reviews. Several research organizations discussed, like Cochrane and Campbell Collaboration, require searches of grey literature to minimize bias. Grey literature is seen as important for capturing context and changes in debates over time and can complement published research.

2. Medical/clinical research
• Traditionally has relied on meta-analysis of
published clinical trials.
• Now there is a strong endorsement for the
consideration of inclusion of unpublished
(grey) trials
• Found in sources like ClinicalTrials.gov
Cochrane Central Register of Controlled Trials
and Current Controlled Trials

3. Conference proceedings
• Trials and studies are often reported in
conference presentations but over one-half of
these never reach full publication
• “Failure to identify trials reported in
conference proceedings might affect the
results or threaten the validity of a systematic
review” (Scherer 2007)

4. Cochrane Collaboration
“Published trials tend to be larger and show
an overall greater treatment effect than grey
trials. This has important implications for
reviewers who need to ensure they identify
grey trials, in order to minimise
the risk of introducing bias into
their review”
(Hopewell, 2007)

5. Campbell Collaboration
• “Campbell reviews must include a systematic
search for unpublished reports (to avoid
publication bias” (Campbell Collaboration, nd)
“Locating studies ..... [search] multiple sources
of grey literature (websites, special registers,
reference lists, listservs, personal
contacts)” (C2 2010)

6. Joanna Briggs Institute
• “In addition to databases of published
research, there are several online
sources of Grey or unpublished literature
that should be considered.”
• “Grey literature has the potential to
complement and communicate findings
to a wider audience, as well as to reduce
publication bias.”
(Thomas, 2008)

7. Health research
• For the evidence base to be comprehensive
and representative … “there is a need to tap
into evidence from the widest variety of
sources, so as to reflect the complexities of
the issue and perceptions of end-users” (Tyndall,
2012)
• Reports, working papers, dissertations, focus
groups, surveys, presentations, opinion polls,
conference papers, crowd-sourcing ...

8. For complex health interventions
GL is needed to fill the information gap
as “an essential part of the evidence
base for practice in complex
interventions, which may have multistakeholders, have multi-variables, have
a lack of predictability and robust data
and require a broad literature approach”
(Simkhada 2004)

9. For policy makers
• policymakers, more than any other
research group, found GL especially
relevant for context, and for its ability to
reflect and map “how debate changes
over time on a particular topic” (AcademyHealth,
2006)
• The recent Australian Dietary Guidelines
consulted over 200 GL sources, making up 20%
of their evidence base. Public consultation +
expert review.

10. Dark data

11. Reusing research data

12. GRAPHC

13. References
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AcademyHealth for the National Library of Medicine. Health Services Research and Health Policy
Grey Literature Project: Summary Report. Bethedsa, Md: National Library of Medicine, 2006.
http://www.nlm.nih.gov/nichsr/greylitreport_06.html#_Toc124061657
Campbell Collaboration. What is a systematic review? [nd]
<http://www.campbellcollaboration.org/what_is_a_systematic_review/index.php>
C2 Training materials 2010
http://www.campbellcollaboration.org/artman2/uploads/1/3_Information_retreival_South_Africa
_2010-8-11.pdf
Hopewell S, McDonald S, Clarke M. et al Grey literature in meta-analyses of randomized trials of
health care interventions. Cochrane Database of Systematic Reviews 2007; Issue 2.
Scherer RW, Langenberg P, von Elm E. Full publication of results initially presented in abstracts.
Cochrane Database of Systematic Reviews 2007, Issue 2.
Simkhada P, Knight J, Reid G, Wyness L, Mandava L. Chasing the grey evidence: a standardised
systematic critical literature review approach: Paper presented at the Sixth International
conference on grey literature “Work on Grey in Progress” 6-7 December 2004, New York
<http://www.opengrey.eu/data/69/78/51/GL6_Simkhada_et_al_2005_Conference_Preprint.pdf>
Thomas P. Shades of grey: the role of grey literature in systematic reviews. PACEsetters: A health
care publication of the Joanna Briggs Institute: promoting and supporting Best Practice 2008; 5: 2223
Tyndall J, Merlin T. Lockwood, C. Impact of findings from grey literature on the outcomes of
systematic reviews on interventions to prevent obesity among children: a systematic review. 2012
JBI Library Systematic Review, JBL000707 (JBI EBP database, viaOvid)