Searching and synthesising 'grey literature' and 'grey information' in public health: critical reflections on three case studies.
BACKGROUND
Grey literature includes a range of documents not controlled by commercial publishing organisations. This means that grey literature can be difficult to search and retrieve for evidence synthesis. Much knowledge and evidence in public health, and other fields, accumulates from innovation in practice. This knowledge may not even be of sufficient formality to meet the definition of grey literature. We term this knowledge 'grey information'. Grey information may be even harder to search for and retrieve than grey literature.


METHODS
On three previous occasions, we have attempted to systematically search for and synthesise public health grey literature and information-both to summarise the extent and nature of particular classes of interventions and to synthesise results of evaluations. Here, we briefly describe these three 'case studies' but focus on our post hoc critical reflections on searching for and synthesising grey literature and information garnered from our experiences of these case studies. We believe these reflections will be useful to future researchers working in this area.


RESULTS
Issues discussed include search methods, searching efficiency, replicability of searches, data management, data extraction, assessing study 'quality', data synthesis, time and resources, and differentiating evidence synthesis from primary research.


CONCLUSIONS
Information on applied public health research questions relating to the nature and range of public health interventions, as well as many evaluations of these interventions, may be predominantly, or only, held in grey literature and grey information. Evidence syntheses on these topics need, therefore, to embrace grey literature and information. Many typical systematic review methods for searching, appraising, managing, and synthesising the evidence base can be adapted for use with grey literature and information. Evidence synthesisers should carefully consider the opportunities and problems offered by including grey literature and information. Enhanced incentives for accurate recording and further methodological developments in retrieval will facilitate future syntheses of grey literature and information.
Present address: Centre for Diet and Activity Research, MRC Epidemiology Unit, University of Cambridge, CB2 0QQ, Cambridge, UK. jma79@medschl.cam.ac.uk.|Institute of Health and Society, Newcastle University, NE2 4AA, Newcastle, UK. jma79@medschl.cam.ac.uk.|Fuse, The Centre for Translational Research in Public Health, Newcastle, UK. jma79@medschl.cam.ac.uk.
Jean
http://orcid.org/0000-0002-5733-7830
J
Adams
Fuse, The Centre for Translational Research in Public Health, Newcastle, UK.|School of Medicine, Pharmacy and Health, Durham University, TS17 3BA, Stockton-on-Tees, UK.
Frances C
FC
Hillier-Brown
Fuse, The Centre for Translational Research in Public Health, Newcastle, UK.|School of Medicine, Pharmacy and Health, Durham University, TS17 3BA, Stockton-on-Tees, UK.
Helen J
HJ
Moore
Fuse, The Centre for Translational Research in Public Health, Newcastle, UK.|School of Medicine, Pharmacy and Health, Durham University, TS17 3BA, Stockton-on-Tees, UK.|Centre for Public Policy & Health, Durham University, TS17 6BH, Stockton-on-Tees, UK.
Amelia A
AA
Lake
Institute of Health and Society, Newcastle University, NE2 4AA, Newcastle, UK.|Fuse, The Centre for Translational Research in Public Health, Newcastle, UK.
Vera
V
Araujo-Soares
Present address: Centre for Diet and Activity Research, MRC Epidemiology Unit, University of Cambridge, CB2 0QQ, Cambridge, UK.|Institute of Health and Society, Newcastle University, NE2 4AA, Newcastle, UK.|Fuse, The Centre for Translational Research in Public Health, Newcastle, UK.
Martin
M
White
Fuse, The Centre for Translational Research in Public Health, Newcastle, UK.|School of Medicine, Pharmacy and Health, Durham University, TS17 3BA, Stockton-on-Tees, UK.
Carolyn
C
Summerbell
Evidence synthesis; Grey information; Grey literature; Interventions; Public health; Systematic review
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