Hand preference observed in large healthy samples: classification, norms and interpretations of increased non-right-handedness by the right shift theory.

Healthy children and undergraduates were observed for hand preference and measured for hand skill in representative samples collected over some years. Writing and throwing were observed for 2844 participants drawn from primary, secondary and higher levels of education. The 12 actions of a standard questionnaire were observed for 2388 secondary school children and undergraduates. These findings provide normative data for comparison with selected samples that may be classified in a variety of ways, including subgroups previously defined and ordered for relative hand skill. Differences between the sexes were found only for certain subgroups of right-mixed-handers. Undergraduates were less variable for hand skill asymmetry than schoolchildren. Interpretations in the light of the RS theory show why statistical effects for comparisons with selected groups are likely to be small. Increased non-right-handedness may be caused by several influences on cerebral dominance, natural and pathological.