Interpreting negative results from an underpowered clinical trial: warts and all.

I N THE RANDOMIZED, PLACEBO-CONTROLLED TRIAL by de Haen et al that appears in this issue of the ARCHIVES, the application of duct tape is compared with placebo as a treatment for common warts. The investigators recruited 103 children in the Netherlands from primary schools and assessed them for warts. Those with warts were randomized to 1 of 2 groups. One group received duct tape to apply to a designated wart, and the other group received a placebo in the form of a corn pad to apply around the wart. The primary outcome of the study was resolution of the designated wart 6 weeks after initiation of therapy. Other outcomes included change in the size of the designated wart and resolution of surrounding warts. Differences in complete resolution of the designated wart were not statistically significant. However, the investigators did find a statistically significant difference in the change in wart diameter: those treated with duct tape had a greater reduction in size compared with the placebo group. Importantly, 15% of the duct tape group stopped treatment early either because of a skin reaction to the treatment or because the tape did not stick well. Given the problems with the duct tape treatment as well as its lack of efficacy, de Haen and colleagues concluded that duct tape has a modest, nonsignificant effect as a therapy for warts.