Handedness in the mentally handicapped.

The prevalence of left-handedness and the degree of handedness were examined in 130 normal and mentally handicapped pupils of both sexes, aged between seven and 18 years. Handedness was assessed by means of 10 performance items. The prevalence of left-handedness among normal pupils (10.6 per cent) was significantly lower than that for the mentally handicapped group (26.5 per cent). There was no significant difference in the prevalence of left-handedness between the mentally handicapped pupils with and without Down's syndrome. The degree of handedness was also reduced in the mentally handicapped group, but again there was no difference between those with and without Down's syndrome.