Moderating Effects of Personality on the Genetic and Environmental Influences of School Grades Helps to Explain Sex Differences in Scholastic Achievement

Abstract

Girls consistently achieve higher grades than boys despite scoring lower on major standardized tests and not having higher IQs. Sex differences in non-cognitive variables such as personality might help to account for sex differences in grades. Utilizing a large sample of 17 year-old twins participating in the Minnesota Twin Family Study (MTFS), we examined the roles of Achievement Striving, Self-Control, and Aggression on sex differences in grade point average (GPA). Each personality trait was a significant predictor of GPA, with sex differences in Aggression accounting for one-half the sex difference in GPA and genetic variance accounting for most of the overlap between personality and GPA. Achievement Striving and Self-Control moderated the genetic and environmental influences on GPA. Specifically, for girls but not boys, higher Achievement Striving and Self-Control were associated with less variability in GPA and greater genetic and environmental overlap with GPA. For girls, certain personality traits operate to shape a context yielding uniformly higher GPA, a process that seems absent in boys.

Figure 1

GPA = grade point average. Standard bivariate behavior genetic model also known as a Cholesky decomposition. A refers to additive genetic effects, C to shared environmental effects, and E to nonshared influences. Factors A₁C₁E₁ include genetic and environmental influences that overlap between Achievement and GPA, while A₂C₂E₂ are genetic and environmental influences unique to GPA. The parameters for each effect are constant.

Figure 2

Ac = Achievement Striving; GPA = grade point average. Model of moderation of genetic and environmental influences on GPA as a function of different levels of Achievement Striving. A refers to additive genetic effects, C to shared environmental effects, and E to nonshared influences. Factors A₁C₁E₁ include genetic and environmental influences that overlap between Achievement Striving and GPA, while A₂C₂E₂ are genetic and environmental influences unique to GPA. Achievement Striving can moderate either the common variance with GPA or the unique variance of GPA. The β's indicate the direction (+ or -) and magnitude of any moderation effects on the paths from the ACE effects to GPA while Ac indicates the level of Achievement Striving.

Figure 3

Variance in Grade Point Average as a function of Achievement Striving for female twins. A refers to additive genetic variance, C to shared environmental variance, and E to nonshared environmental variance.

Figure 4

Variance in Grade Point Average as a function of Self-Control for female twins. A refers to additive genetic variance, C to shared environmental variance, and E to nonshared environmental variance.

Figure 5

Variance in Grade Point Average as a function of Achievement Striving for male twins. A refers to additive genetic variance, C to shared environmental variance, and E to nonshared environmental variance.