Difficult Temperament and Externalizing Behavior Problems in Preschool

Difficult Temperament and Externalizing Behavior Problems in Preschool: A Genetically Informed Cross-Lagged Model Model • There is substantial evidence supporting an association between externalizing behavior problems (EXT) and difficult temperament (DIFF) (e.g., Guerin, Gottfried, & Thomas, 1997; Oberklaid, Sanson, Pedlow, & Prior, 1993). 0.9 • Genetically informed cross-lagged models provide information about the genetic and environmental contributions to the relation between traits within and across ages, as well as the stability of each trait (Figure 3). Intraclass Correlations Introduction Table 2. Genetic, Shared Environmental, and Nonshared Environmental Influences on EXT and DIFF at Age 3 1 0.8 0.7 0.6 MZ DZ 0.5 0.4 0.3 0.2 0.1 A C E Total ACE variance due to: .609 .061 .330 EXT age 2: stability effects .187 (30.6%) .012 (2.0%) .077 (12.6%) .334 (54.8%) .054 (88.9%) .007 (11.1%) - .053 (16.1%) .003 (0.91%) .007 (11.0%) .266 (80.7%) Total ACE variance due to: .634 .088 .279 DIFF age 2: stability effects .145 (22.9%) .164 (2.6%) .079 (12.5%) .393 (61.9%) .083 (94.3%) .005 (5.7%) - .036 (12.9%) .005 (1.7%) .007 (2.5%) .023 (82.8%) EXT AGE 3 0 • Little attention has been paid to the genetic and environmental influences on the longitudinal stability and bidirectionality of these behaviors. • The cross-lagged paths reflect the independent impact of traits across age above and beyond their preexisting association. Goal • The present study seeks to uncover the direction of effect between EXT and DIFF and whether there is genetic and environmental overlap between these phenotypes both within and across ages. • The stability paths across ages index the stability of EXT and DIFF while controlling for any prior association between the phenotypes. • Both phenotypes at age 2 and the effects at age 3 that are independent of prior effects were decomposed into genetic (A), shared (C), and nonshared (E) environmental estimates. Figure 1. BUTP Participants Methods Sample • 145 monozygotic (MZ) and 169 dizygotic (DZ) samesex twin pairs assessed within approximately 2 weeks of their 2nd and 3rd birthdays. EXT 2 DIFF 2 EXT 3 DIFF 3 Figure 2. Twin Intraclass Correlations Common effects at age 2 • For all measures at both ages, the intraclass correlations (Figure 2) for MZ twins exceeded those of DZ twins, suggesting that genetic influences contribute to individual differences in each trait. Model-Fitting Results Stability effects Cross-lagged effects Common effects from age 2 Specific age 3 effects • Temperament. Parents rated the temperament of each child on the Toddler Behavior Assessment Questionnaire (TBAQ; Goldsmith, 1996). Difficult Temperament Composite • Factor analysis on the TBAQ indicated a clear difficult temperament factor. The standardized composite included the activity level, anger, sadness, and reverse-scored soothability, and inhibitory control subscales. • The difficult temperament composite was created using the average of the standardized Z-scores. • Both phenotypes at age 2 were influenced by genetic, shared environmental, and nonshared environmental factors. Table 1. Phenotypic Correlations Between EXT and DIFF at Ages 2 and 3 Age 3 DIFF - Note. A=Genetic influences; C=Shared environmental Influences; E=Nonshared environmental influences. Percentages of genetic, shared environmental, and nonshared environmental influences due to four sources are provided in parentheses. Figure 3. Standardized path estimates for the genetic (A), shared environmental (C), and nonshared environmental (E) factors from the bestfitting cross-lagged model. Dashed paths indicate nonsignificant parameters that were dropped from the model. Solid paths were retained in the bestfitting reduced model. Correlations EXT EXT age 2: cross-lagged effects Conclusions Results Age 2 - DIFF AGE 3 Specific effects at age 3 Measures • Externalizing Behavior Problems. The Child Behavior Checklist/1½ - 5 (CBCL; Achenbach & Rescorla, 2000) provided a measure of externalizing behavior problems. Specific effects at age 3 Common effects at age 2 • This model allows us to understand the extent to which EXT and DIFF influence each other over time by portioning the genetic and environmental variance in each phenotype at age 3 into four different effects: 1. 2. 3. 4. DIFF age 2: cross-lagged effects EXT EXT age 2 1 DIFF age 2 .54 1 EXT age 3 .66 .44 1 DIFF age 3 .45 .65 .60 • At both ages there were significant genetic and nonshared environmental correlations between EXT and DIFF. DIFF • For both constructs at age 3, there were new genetic and nonshared environmental factors, but no new shared environmental influences independent of the age 2 effects. 1 • The cross-lagged and stability paths were all significant, suggesting that there is stability in both variables across time and that there is a bidirectional relation between these phenotypes from age 2 to age 3. These effects are primarily due to genetic factors (Table 2). Note. All correlations are significant at p < .0001 • As indicated in Table 1, EXT and DIFF showed considerable stability across age and were related within and across age. • Parent ratings of externalizing behavior problems and difficult temperament are stable and interrelated across age. • Genetic variance largely accounts for stability and cross-lagged effects for both behaviors. • Although the stability and cross-lagged effects contribute to genetic and environmental influences in externalizing behavior problems and difficult temperament at age 3, new genetic and nonshared environmental effects emerge at age 3 and are substantial. • These findings highlight the bidirectional nature between externalizing behavior problems and difficult temperament in early childhood, however, novel effects at age 3 illustrate the importance of developmental change at the level of etiology.