Genetic and environmental influences on item response pattern scalability.

Numerous studies have examined how genetic and environmental factors determine individual differences on multi-item personality scales. Few studies, however, have examined how genes and the environment influence the route by which individuals obtain their scores on these scales. Specifically, on a multi-item test, dozens of item response patterns result in equivalent total scores, though some response patterns are more likely to be observed than others. For many scales it may be of interest to determine the genetic and environmental influences on the item response patterns, as well as the sum of the item responses. We discuss a latent trait measure of item response pattern scalability, called Zl (Levine and Drasgow, 1982), and investigate the properties of this index from a behavioral genetics perspective. Using a large sample of identical and fraternal twins from the Minnesota Twin Registry (Lykken et al., 1990), item response pattern scalability is shown to be moderately heritable. On the four scales of the Multidimensional Personality Questionnaire (Tellegen, 1982) that were investigated, approximately 20% of the variation in scalability was due to genetic diversity between subjects of our sample. Follow-up analyses, using a factor-analytically based, genotype-environment model of item response behavior, indicated that specific genetic and environmental factors play a substantial role in determining item response pattern variation.