Association Between Publication Characteristics and Treatment Effect Estimates: A Meta-epidemiologic Study.

BACKGROUND

Evidence about the effect on meta-analysis results of including unpublished trials or those published in languages other than English is unclear or discordant.

PURPOSE

To compare treatment effects between published and unpublished randomized controlled trials (RCTs) and between trials published in English and other languages using a meta-epidemiologic approach.

DATA SOURCES

Cochrane reviews published between March 2011 and January 2017 and trial references cited in the reviews.

STUDY SELECTION

RCTs included in meta-analyses of 3 or more trials with a binary efficacy outcome.

DATA EXTRACTION

Trial characteristics were extracted by original review authors. A single reviewer assessed publication status and language, with quality assurance by another investigator.

DATA SYNTHESIS

Among 5659 RCTs included in 698 meta-analyses, 5303 (93.7%) were published in journal articles and 356 (6.3%) were unpublished. Of journal articles, 92.6% (4910 of 5303) were published in English and 7.4% (393 of 5303) in another language. Treatment effects were larger in published than unpublished trials (combined ratio of odds ratios [ROR] for 174 meta-analyses, 0.90 [95% CI, 0.82 to 0.98]; I2 = 19.3%; τ2 = 0.0492). Treatment effects were also larger for trials published in a language other than English than in English (combined ROR for 147 meta-analyses, 0.86 [CI, 0.78 to 0.95]; I2 = 0%; τ2 = 0.0000).

LIMITATION

Reliance on the primary reference cited by review authors as the record of interest.

CONCLUSION

In meta-analyses, treatment effects were larger in published than unpublished trials and, for published trials, in those published in a language other than English than in English.

PRIMARY FUNDING SOURCE

Cochrane France.