Age and cohort effects in adult handedness.

A systematic increase with age of the strong right-handers/mixed right-handers ratio, in normal adults, was found in Algeria, Greece, Italy, France and Spain. This age effect on adult handedness is not easily explained by variations in the social pressure against left-hand use, differential mortality, or information bias. There was no systematic decrease in the frequency of left-handedness with age. Left-hand writing among left-handers was common in the youngest age group and rare after 40 years of age.