Abstract
Many studies have documented that cognitive performance is often higher among people of the same age who are tested in more recent years, and it is sometimes suggested that this phenomenon will distort the relations between age and cognition in cross-sectional studies. This possibility was examined with data from two large projects involving adults across a wide age range. The results indicated that there were similar time-of-measurement increases in cognitive scores at different ages, which were accompanied by nearly constant cross-sectional age differences, but positively inflated estimates of longitudinal age differences. It is proposed that when the Flynn Effect is of comparable magnitude in adults of different ages, longitudinal comparisons of age-cognition relations are more subject to distortion than cross-sectional comparisons.