The influence of nonshared environmental factors on number and word recall test performance

• We used MZ difference scores analysis to examine the influence of nonshared environments on adult recall ability.
• None of the nonshared environments were found to be consistently related to recall ability.
• We discuss the implications of these findings for research examining the development of recall ability and intelligence.

A large body of research indicates that variation in intelligence is influenced by genetic and environmental factors. Despite this knowledge, much of the research examining environmental influences on intelligence is not conducted using genetically informative research designs. In order to address this gap in the literature, this study examines the potential association between nonshared environments and measures of intelligence (recall ability) in adulthood using monozygotic (MZ) difference scores analyses. Analysis of MZ twin pairs drawn from the National Longitudinal Study of Adolescent to Adult Health revealed that none of the nonshared environmental variables were consistently related to recall ability. One nonshared environmental variable, maternal disengagement, was found to be a significant predictor of recall ability in two of the four recall tasks. In addition, measures of maternal attachment and delinquent peers were found to be associated with only one test of word recall ability and none of the three other recall tests.