The diminished number of older left-handers: differential mortality or social-historical trend?

Recent research suggests that left-handers have shorter life spans. This interpretation could be erroneous if there is a social-historical trend in handedness with older individuals more frequently switched to right-handedness. This would result in fewer older left-handers due to social factors. Two samples (N = 1960 and N = 8526), separated by a 12 year interval were tested. Social-historical hypotheses predict that the later sample should have higher proportions of left-handedness. Although both samples showed decreased sinistrality with age, there was no increase in the proportion of left-handers over the 12 year period, suggesting that the rarity of older left-handers is due to reduced longevity.