Age differences within secular IQ trends: An individual growth modeling approach

Age differences within the yo-yo trend in IQ, caused when aging norms that produce inflated scores are replaced with new norms, were examined using longitudinal WISC, WISC-R and WISC-III records of students tested for special education services from 10 school districts. Descriptive and individual growth modeling analyses revealed that while the secular pattern in IQ has not changed over time, the role of age within this pattern has. Specifically, the decline in test scores that occurs when new norms replace older ones was smaller for older children in earlier testings. These differences, however, disappeared in more current testings. The results reveal that the relationship between IQ and age is complex and, further, shows the benefits of using individual growth modeling to uncover patterns within longitudinal data that would otherwise be obscured with more traditional analytic techniques.