Empirical evidence for outcome reporting bias in randomized clinical trials of acupuncture : comparison of registered records and subsequent publications

Background: Outcome reporting bias has received widespread recognition and been considered to pose two threats to the validity of clinical decision making because they overestimate the effect of treatments or distort the results of trials. However, the problem of outcome-reporting bias has not been systematically studied among randomized clinical trials of acupuncture. Our objectives were to evaluate the consistency between the registered records and subsequent publications with respect to outcomes and other data as well as to determine whether outcome-reporting bias favors significant primary outcomes. Methods: A systematic search of 15 registries was conducted from their inception to January 2014 to identify randomized clinical trials on acupuncture for which the status was listed as 'completed.' The subsequent publications were retrieved by searching PubMed and three Chinese databases. Basic characteristics and the registration information were extracted from the registered records and publications. We performed comparisons regarding primary outcomes and other data between the registered records and subsequent publications to assess the consistency and selective outcome reporting. Results: Eighty-eight trials on acupuncture with 96 published reports were identified. Only 19.3% (17/88) were registered before the start of the trial, suggesting prospective registration. The trial registration number was unavailable in 36 published reports (37.5%). A comparison of registered and published primary outcomes could be conducted in 71 publications (74.0%), and the inconsistency of the primary outcomes was identified in 45.1% (32 of 71); 71.4% (15 of 21) had a discrepancy that favored statistically significant primary outcomes, while 28.6% (6 of 21) favored nonsignificant primary outcomes. Furthermore, the other inconsistencies between the registry records and subsequent publications involved the inclusion criteria (54.7%), exclusion criteria (47.9%) and controls (22.9%). Conclusions: We find that prospective registration for randomized clinical trials on acupuncture is insufficient, selective outcome reporting is prevalent, and the change of primary outcomes is intended to favor statistical significance. These discrepancies in outcome reporting may lead to biased and misleading results of randomized clinical trials on acupuncture. To ensure publication of reliable and unbiased results, further promotion and implementation of trial registration are still needed.