Handedness in Swedish 10-year-olds. Some background and associated factors.

Forty-five left-handed and 46 right-handed 10-year-old children were subjected to a limited set of neurological tests and a square tracing task. 'Pathological' handedness was diagnosed in cases showing poor performance with the non-preferred hand on the squares task. The frequency of left-handedness in the population was estimated at 9.2%. The boy : girl ratio was 1.6:1. 'Pathological' handedness was twice as common among left-handers as among right-handers. Neurological dysfunction was more common in 'pathological' handers, especially left-handers. Reduced pre-. peri- and neonatal optimality was seen in boys with 'pathological handedness'. School achievement problems and behaviour problems were much more common in left-handed boys than in other study groups. The results lend partial support for the extended pathological left-handedness model recently hypothesized by Bishop, but it is suggested that left-handedness in boys is more often a symptom of pathological shift of handedness than is left-handedness in girls.