Prospective registration, bias risk and outcome-reporting bias in randomised clinical trials of traditional Chinese medicine: an empirical methodological study

BACKGROUND: Clinical trials on Traditional Chinese Medicine (TCM) should be registered in a publicly accessible international trial register and report on all outcomes. We systematically assessed and evaluated TCM trials in registries with their subsequent publications. OBJECTIVE: To describe the characteristics of TCM trials, estimate bias risk and outcome-reporting bias in clinical trials. DATA SOURCES AND STUDY SELECTION: Fifteen trial registries were searched from their inception to July 2012 to identify randomised trials on TCM including Chinese herbs, acupuncture and/or moxibustion, cupping, tuina, qigong, etc. DATA EXTRACTION: We extracted data including TCM specialty and treated disease/conditions from the registries and searched for subsequent publications in PubMed and Chinese databases. We compared information in the registries of completed trials with any publications focusing on study design, sample size, randomisation, bias risk including reporting bias from the register protocol. RESULTS: 1096 registered randomised trials were identified evaluating TCM, of which 505 were completed studies (46.1%). The most frequent conditions were pain (13.3%), musculoskeletal (11.7%), nervous (8.7%), digestive (7.1%), circulatory (6.5%), respiratory (6.3%), mental and behavioural disorders (6.2%) and cancer (6.0%). The trial register data identified parallel, phase II/III randomised trials with sample size estimations and blinding, but limited information about randomisation (sequence generation and allocation concealment). Comparing trial registration data of 115 completed trials (22.8%) with their subsequent 136 publications, inconsistencies were identified in one or more of the following: sample size (11%), outcome assessor blinding (37.5%), primary outcomes (29%) and safety (28%) reporting. CONCLUSIONS: Increasing numbers of clinical trials investigating a variety of TCM interventions have been registered in international trial registries. The study design of registered TCM trials has improved in estimating sample size, use of blinding and placebos. However, selective outcome reporting is widespread and similar to conventional medicine and therefore study conclusions should be interpreted with caution.