We described study characteristics according to sample size, characteristics of study participants, study duration, duration of treatment, and source of funding. For trials with more than two intervention groups, we extracted data for the maximum dose of varenicline (that is, 1 mg twice daily) and the placebo group. The “metan” command in Stata (version 13, StataCorp, USA) was used to conduct all of the meta-analyses.18 Because our outcomes of interest are rare, we followed recommendations of Bradburn and colleagues19 and used Peto odds ratios to compare the varenicline and placebo groups. We also undertook meta-analyses using Mantel-Haenszel risk differences. We report results including 95% confidence intervals and forest plots for both measures so that findings can be compared. Statistical heterogeneity was assessed with the I2 statistic.20
