Reply to the Response to The Statistics of Skin Impedance

Dear Editor:

We thank Colbert et al. for their contribution to the nature of the statistics of skin bioimpedance, ¹ which answered our previous letter on the subject. ² However, we feel obliged to comment on their letter, otherwise a subtle misunderstanding may take place in this important matter. Indeed, the log-normal distribution of bioimpedance is observed across individuals in a population and not on a sample of measurements performed at different points on the skin of an individual. In this way, the consideration of Bouscein ³ of not making mathematical transformations on the raw skin impedance data in electrodermal devices is appropriate, since their objective is to compare bioimpedances in a single individual.

To conclude, we must be aware of the statistical analysis of bioimpedance for two distinct experimental designs: the first is intended to study the impedance for a unique individual (for instance, when studying the low impedance of acupoints in comparison to neighbor points for a given individual). The second approach consists of comparing skin impedance along a sample of individuals: At this point we should take into account the log-normal distribution of the data.