summary level, for example, through publication in a peer-reviewed journal or through publicly accessible clinical trial registration sites (e.g., ClinicalTrials.gov). Other data, however, remain largely unavailable to outside researchers and the public, including data found in analyzable data sets, clinical study reports (CSRs), and individual participant data (IPD) that, if accessible, could facilitate new analyses and a deeper understanding of a particular therapy or condition (Doshi et al., 2013; Goldacre, 2012; Gordon et al., 2013; Rawlins, 2012). Increased sharing of IPD, in particular, could facilitate activities such as independent reanalysis of trial results, addressing concerns about publication bias,2 characterizing trial outcomes by subgroups, considering additional questions beyond the original trial hypotheses, carrying out meta-analysis for systematic reviews, and facilitating hypothesis generation and additional research to develop new therapies (Doshi et al., 2012; IOM, 2013; McGauran et al., 2010; Ross et al., 2012).
The data sharing movement has gained substantial momentum during the last decade, in both the clinical trial and larger scientific communities (Boulton et al., 2011; Royal Society, 2012). A cultural change has occurred in which the conversation around data sharing has moved from whether it should happen to how it can be carried out (IOM, 2013). To that end, a large number of people and organizations involved in clinical trials have endorsed principles promoting, in their view, responsible sharing of clinical trial data (Loder, 2013). Prominent examples include the joint statement from funders of health research data, the AllTrials campaign, and the Pharmaceutical Research and Manufacturers of America (PhRMA) and European Federation of Pharmaceutical Industries and Associations (EFPIA) principles (AllTrials, 2013; PhRMA and EFPIA, 2013; Wellcome Trust, 2011). Some organizations have gone beyond general statements and principles and begun to adopt data sharing policies as well. The U.S. National Institutes of Health (NIH), as well as international groups of researchers and nonprofit funders, has been involved in data sharing activities for years (e.g., BioLINCC, MalariaGen). More recently, European regulators and some pharmaceutical and device companies (e.g., GlaxoSmithKline [GSK], Medtronic) have begun to plan and implement their own data sharing policies (EMA, 2013; Nisen and Rockhold, 2013; YODA, 2013). In addition, medical journals have begun to require authors to include data sharing statements
2 The tendency for positive results of trials of health care interventions to be reported or published, with corresponding underreporting/non-publication of negative or inconclusive results (Cochrane Collaboration, 2002).