Risk assessments were performed using data from a number of sources (as available) including trial primary publications, trial design manuscript, trial protocol, and trial presentations.
We found several factors associated with non publication: Trials sponsored by industry were less likely to have result publications than trials with other funding sources, indicating that conflict of interest may be a factor in non publication.
To achieve a larger proportion of trials with subsequent publication, trials registered after January 2009 were not included.
Despite considerable recent efforts to implement measures to reduce the non-publication of trials, publication bias is still a major problem in medical research.
Non publication trial is a more serious problem in China than in other countries.
Regulatory submission, trial publication, trial registration, and systematic review produce unstructured datasets that are insufficient for supporting evidence-based decision making.
A data extraction form was designed previously, and included the following items: general identification information (authors, title, journal, date of publication, protocol name, and duplication of publication), trial, type of patients, intervention characteristics, and reported outcomes.
Four retention trial publications contained two trials each.
Four retention trial publications contained two trials each (Khadjesari 2011; McCambridge 2011; McColl 2003; Severi 2011).
No significant differences in reporting of any or all elements were detected between publications of trials with industry and nonindustry sponsorship.
Full journal publications of trials were sought with no language restriction.
