Materials and Method

48 boys and 47 girls took part in the stratified study. 4–5 pupils came randomly from 3 to 12 school classes, ages 8 to 19 years. All of them had passed a test at the entrance to the school, which included reproducing a rhythm by clapping, repeating tones by singing, and singing a given song (Figs. 3.1 and 3.2) as it is done by others [1]. The tests were also used for determining the type of voice (the voice category) because hormonal changes were thought eventually to be related. The test was necessary to define a standard of the study for comparison with other studies but was later considered without specific influence on the general results. Video analysis showed no neoplasms or other anatomic abnormalities of the larynx for all of them. The Tanner stage of puberty was measured by our pediatrician for the age of each pupil [2, 3].