Classifying speech into normal and disordered is more problematic than it first seems. By a strict classification, only 5% to 10% of the population have a completely normal (with respect to all parameters) and healthy voice, all others suffer from one disorder or another. Dysphonia, that is, incomplete functionality of the vocal folds, is one of the most common and can be observed as, for example, an unusual roughness of the voice. Stuttering is also quite common, about 7% of the population suffer from it at some point in life.
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