About 5 per cent of children under the age of five will experience dysfluent speech while learning to talk and about a quarter of them develop chronic stuttering. Stuttering is more common in boys than in girls. Stuttering varies in degree of severity and according to the situation. It is episodic. For example, a child may be fluent for days or weeks at a time then dysfluency can reappear.
Adults commonly report good days and bad days.
It is well known that some speaking conditions reduce stuttering severity. Stuttering will be reduced or eliminated when the person is singing or speaking in a chorus, but stuttering will reappear as soon as the situation changes.