title: Exploring changes over time and characteristics associated with data retrieval across individual participant data meta-analyses: systematic review.
abstract: ObjectiveTo investigate whether the success rate of retrieving individual participant data (IPD) for use in IPD meta-analyses has increased over time, and to explore the characteristics associated with IPD retrieval.DesignSystematic review of published IPD meta-analyses, supplemented by a reflection of the Cochrane Epilepsy Group's 20 years' experience of requesting IPD.Data sourcesMedline, CENTRAL, Scopus, Web of Science, CINAHL Plus, and PsycINFO.Eligibility criteria for study selectionIPD meta-analyses of studies of all designs and all clinical areas published in English.Results760 IPD meta-analyses which identified studies by systematic methods that had been published between 1987 and 2015 were included. Only 188 (25%) of these IPD meta-analyses retrieved 100% of the eligible IPD for analysis, with 324 (43%) of these IPD meta-analyses retrieving 80% or more of relevant IPD. There is insufficient evidence to suggest that IPD retrieval rates have improved over time. IPD meta-analyses that included only randomised trials, had an authorship policy, included fewer eligible participants, and were conducted outside of the Cochrane Database of Systematic Reviews were associated with a high or complete IPD retrieval rate. There was no association between the source of funding of the IPD meta-analyses and IPD retrieval rate. The IPD retrieval rate of the Cochrane Epilepsy Group has declined from 83% (up to 2005) to 65% (between 2012 and 2015) and the reported reasons for lack of data availability have changed in recent years.ConclusionsIPD meta-analyses are considered to be the "gold standard" for the synthesis of data from clinical research studies; however, only 25% of published IPD meta-analyses have had access to all IPD.
authors.affiliation: Department of Biostatistics, University of Liverpool, Liverpool L69 3GL, UK sjn16@liverpool.ac.uk.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Nevitt
authors.affiliation: Department of Molecular and Clinical Pharmacology, University of Liverpool, Liverpool, UK.
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Marson
authors.affiliation: Department of Biostatistics, University of Liverpool, Liverpool L69 3GL, UK.
authors.forename: Becky
authors.initials: B
authors.lastname: Davie
authors.affiliation: Department of Biostatistics, University of Liverpool, Liverpool L69 3GL, UK.
authors.forename: Sally
authors.initials: S
authors.lastname: Reynolds
authors.affiliation: Department of Biostatistics, University of Liverpool, Liverpool L69 3GL, UK.
authors.forename: Lisa
authors.initials: L
authors.lastname: Williams
authors.affiliation: Department of Biostatistics, University of Liverpool, Liverpool L69 3GL, UK.
authors.forename: Catrin Tudur
authors.initials: CT
authors.lastname: Smith
mesh_terms: D006801:Humans; D016247:Information Storage and Retrieval / Q000379:methods / Q000639:trends*; D015201:Meta-Analysis as Topic; D035842:Research Subjects