A double-blind, randomized, placebo-controlled, two-dose comparative study of botulinum toxin type A for treating glabellar lines in Japanese subjects: what if sample size and statistical tests mattered?

摘要

We read with interest the article published by Harii and Kawashima [1]. While the authors are to be commended for investigating the effect of different doses of botulinum toxin type A (BTX-A) in Japanese subjects, there are several issues with both the design of the study and the statistical analysis used. With respect to the study design, despite the statement from the authors that it was a prospective, randomized, double-blind, placebo-controlled-study, it does not appear to be so. There was no hypothesis to test; it appears to be a pilot study. Even if the authors wanted to test the hypothesis that halving the dose of BTX-A (from 20 to 10 U) would not result in a significant decrease in a patient's response rate, the sample size calculation is still missing. In fact, in order for a particular finding to be claimed as significant (or not), the study must have enough power. The authors do not state anything about the expected change in response rate values and therefore it is almost impossible to perform a prestudy sample size calculation. However, it is possible to perform a post-hoc sample size calculation or power analysis on the statistical tests they have used from their data.