"The IQ gains of the 20th century have faltered"

When a later cohort is compared to an earlier cohort, IQ trends vary dramatically by age. Piagetian trends indicate that a decimation of top scores may be accompanied by gains in cognitive ability below the median. They also reveal the existence of factors that have an atypical impact at high levels of cognitive competence. Scandinavian data from conventional tests confirm the decimation of top scorers but not factors of atypical impact. Piagetian tests may be more sensitive to detecting this phenomenon.