RESEARCH ARTICLE v

Full list of author information is available at the end of the articletrials is controversially discussed in the literature. Re-views on this effect have been published in the past, but these have usually focused on comparisons between ‘trial patients ’ and ‘non-trial patients ’ and authors have come to conflicting conclusions [1-3]. Pater et al. [5], especially from the healthcare policy per-spective, this question should be the main focus of fu-ture research because benefit from a research-active institution will affect many more patients than just the small proportion of participants in clinical trials. In addition, this issue may also be of greater importance to patients who have to decide where to go to receive * Correspondence: rochon@imbi.uni-heidelberg.de1Institute of Medical Biometry and Informatics, University of Heidelberg,healthcare providers who are willing to participate inoutcomes than patients treated in research-inactive institutions. However, little attention has been paid to explaining such effects, probably because techniques for mediation analysis existing so far have not been applicable to survival data. Methods: We investigated the underlying mechanisms using a recently developed method for mediation analysi