Clinical trial registration at Tobacco Control

Systematic reviews and meta-analyses of randomised controlled trials are the most methodologically rigorous types of evidence to evaluate the effectiveness of therapeutic interventions, particularly pharmacotherapy. 1, 2 They often form the foundation for practice guidelines, clinical decision support systems, drug formulary decisions and drug payment schemes. Several studies based on self-reports from authors with unpublished studies conclude that authors are responsible for most of the observed publication bias, as they do not submit their statistically non-significant studies for publication in the first place. 5- 7, 13 A recent prospective cohort study of 1107 manuscripts submitted to three major medical journals found that a statistically significant primary outcome did not improve a paper's chance of publication, although the type of study design, large sample size and some author characteristics were predictive of publication. 14 Selective reporting of results can also distort the research record.