Study	Reason for exclusion
Burrett 2003	149 trials in childhood acute lymphoblastic leukaemia were identified from international trial registries and by searching MEDLINE. This study was excluded because of the potential for bias in the sample of trials identified as it only included published reports of trials and did not track the publication status of all the registered trials. The analysis of time to publication was also not available separately for positive and negative/null trials.
Cronin 2004	101 research studies commissioned by the North Thames Region of the NHS R & D Programme in the UK between 1993 and 1998 were assessed. The median time to publication from completion of follow up to publication in a peer reviewed journal was 35 months. This study was excluded because not all of the research studies were reports of clinical trials. The analysis of time to publication was also not available separately for positive and negative/null trials.
Liebeskind 1999	127 published trials in acute ischaemic stroke were identified from international trials registries and by searching MEDLINE. The median time from enrolment of first patient to publication was 4.2 years (positive trials 3.5 years, null/negative trials 4.4 years). This study was excluded because of the potential for bias in the sample of trials identified as it only included published reports of trials.
Misakian 1998	84 studies into the effects of passive smoking were identified through organisations known to fund research into passive smoking (1981‐1995). The median time from the year the grant was obtained to first publication was 3 years for studies with positive results, 5 years for non‐significant results and 7 years for null studies. This study was excluded because it did not include clinical trials. Although studies involving humans were analysed separately to those involving animals it was anticipated that the factors influencing time to publication of non‐clinical research studies might be different to those influencing clinical trials.
Simes 1987	Registered trials and published trials evaluating the effectiveness of chemotherapy on survival in advanced breast cancer were assessed. The cohort of registered trials were identified from protocols registered with the International Cancer Data Bank before October 1987. The cohort of published trials was identified by searching MEDLINE and conference proceedings prior to October 1987. This study was excluded because the analysis of time to publication was not available separately for the registered cohort of trials and the published cohort of trials.