Effects of nonpathogenic gram-negative bacteriumVitreoscilla filiformislysate on atopic dermatitis: a prospective, randomized, double-blind, placebo-controlled clinical study. Does this make a real difference?

Conflicts of interest: none declared. Sir, We read with interest the article published by Drs Gueniche et al.1 While the authors are to be commended for their aim to conduct a prospective, randomized, double‐blind, placebo‐controlled trial about the effect of a nonpathogen bacterium on the course of atopic dermatitis, there are some issues with both the design of the study and the statistical analysis used. As for study design, the major issue is that there is no reference to any sample size calculation. In fact, in order for a particular finding to be claimed as significant (or not), the study should be powered enough. In this particular case, the authors do not state anything about the expected change in SCORing of Atopic Dermatitis (SCORAD) and visual analogue scale (VAS) scores. Therefore, it is almost impossible to perform a pre‐study sample size calculation (at least, we could not). Similarly, as the authors do not provide any tables describing their data, it is almost impossible to perform a post‐hoc sample size calculation or power analysis on the statistical tests they have used. However, given the significant overlap of VAS scores in the groups (see Fig. 4 in the referenced paper1), a total sample of 75 patients might not have been sufficient to make inferences with a real significance (e.g. considering the ‘standard’α error of 0·05 and a power of 0·8). As the authors do actually draw conclusions from their data, could they confirm the correctness of their sample size calculation or provide the power and level of significance of each test given a total sample of 75 patients?