Using Item Response Theory to assess the Flynn Effect in the National Longitudinal Study of Youth 79 Children and Young Adults data

Abstract

The purpose of this manuscript is to assess the magnitude of the Flynn Effect (i.e., increase in mean IQ scores across time) using Item Response Theory (IRT). Unlike using methods derived from Classical Test Theory, IRT has the capability to determine if the Flynn Effect is due to a genuine increase in intelligence, if it is due to a psychometric artifact (i.e., items changing properties over time), or a combination of the two. Using the Peabody Picture Vocabulary Test—Revised and Peabody Individual Achievement Test—Math from the National Longitudinal Study of Youth 79 Children and Young Adults, the results of this study indicate that while using raw and standardized scores, the Flynn Effect is evident in a predicted magnitude, but when using scores based from IRT analysis, the magnitude Flynn Effect substantially decreases, and, at least for the Peabody Picture Vocabulary Test—Revised, goes away. Thus, for the data used in this study, the Flynn Effect appears to be largely the result of changing item properties instead of changes in cognitive ability.