Pilometric methods-contributions and critical aspects.

On the basis of 13,000 single-hair-measurements and their statistical data a sample-size of 100 hair-measurements could be proved as an absolute minimum for the determination of the individual hair-thickness. If the standard deviation of a hair sample exceeds 15 mu its size should be increased accordingly. All the individual determinations of hair-thickness basing on samples consisting of less than 100 single hairs will lead to false results. In order to test if the measurements of hair-cross-section and of longitudinal top plan view result in approximately equal, constant, individual means, one part of the hairs of each of the samples was measured according to the cross-section, the other part according to the longitudinal method; into more than 10,000 single hairs thus have been studied. The means of the corresponding samples are within the expected confidence intervals. There exists consequently no difference between the results of the two measuring methods. Nevertheless both procedures require at least measurements of 100 unselected single hairs per sample in order to obtain individual representative means. Practicability of direct square-measurements and indirect calculation methods are shown, their advantages as well as their disadvantages discussed. Attention is drawn to much more correct calculation formula.