Michael A. Woodley, Guy Madison, Bruce G. Charlton. Possible Dysgenic Trends in Simple Visual Reaction Time Performance in the Scottish Twenty-07 Cohort: A Reanalysis of Deary & Der (2005). Mankind Quarterly. In press.
In a 2005 publication, Deary and Der presented data on both longitudinal and cross-sectional aging effects for a variety of reaction time measures among a large sample of the Scottish population. These data are reanalyzed in order to look for secular trends in mean simple reaction time performance. By extrapolating longitudinal aging effects from within each cohort across the entire age span via curve fitting, it is possible to predict the reaction time performance at the start age of the next oldest cohort. The difference between the observed performance and the predicted one tells us whether older cohorts are slower than younger ones when age matched, or vice versa. Our analyses indicate a significant decline of 36 ms over a 40-year period amongst the female cohort. No trends of any sort were detected amongst the male cohort, possibly due to the well-known male neuro-maturation lag, which will be especially pronounced in the younger cohorts. These findings are tentatively supportive of the existence of secular declines in simple reaction time performance, perhaps consistent with a dysgenic effect. On the basis of validity generalization involving the female reaction time decline, the g equivalent decline was estimated at -7.2 IQ points, or -1.8 points per decade.
This is the full paper publication of some results previously reported here: