Dropouts in randomized clinical trials of Korean medicine interventions: a systematic review and meta-analysis

Background: The dropout rate is an important determinant of outcomes in randomized controlled trials (RCTs) and should be carefully controlled. This study explored the current dropout rate in studies of Korean medicine (KM) interventions by systematic evaluation of RCTs conducted in the past 10years. Methods: Three clinical trial registries (Clinical Research Information Service, ClinicalTrials.gov, and World Health Organization International Clinical Trials Registry Platform) were searched to identify RCT protocols for KM interventions, such as acupuncture, herbal medicine, moxibustion, or cupping, and studies of mixed interventions, registered in Korea from 2009 to 2019. The PubMed, Embase, and OASIS databases were searched for the full reports of these RCTs, including published journal articles and theses. Dropout rates and the reasons for dropping out were analyzed in each report. The risk of bias in each of the included studies was assessed using the Cochrane risk of bias tool. The risk difference for dropping out between the treatment and control groups was calculated with the 95% confidence interval in a random effects model. Results: Forty-nine published studies were included in the review. The median dropout rate was 10% in the treatment group (interquartile range 6.7%, 17.0%) and 14% in the control group (interquartile range 5.4%, 16.3%) and was highest in acupuncture studies (12%), followed by herbal medicine (10%), moxibustion (8%), and cupping (7%). Loss to follow-up was the most common reason for dropping out. The risk difference for dropping out between the intervention and control groups was estimated to be 0.01 (95% confidence interval -0.02, 0.03) in KM intervention studies. Conclusions: This review found no significant difference in the dropout rate between studies according to the type of KM intervention. We recommend allowance for a minimum dropout rate of 15% in future RCTs of KM interventions. Review protocol registration: PROSPERO CRD42020141011