KHT (all papers) and DG and RMM (papers equally shared) performed double data extraction to collect information on the study design (duration of treatment, description of allocation concealment, and blinding), study participants (inclusion and exclusion criteria, country, region, population studied, and baseline characteristics such as ethnicity, sex, smoking history), description of the intervention and placebo groups, primary and secondary outcomes, measures of efficacy of treatment, losses to follow-up, and study sponsor. KHT contacted authors of all studies to verify the accuracy of the extracted data.
