Substantial genetic influences on Cloninger’s temperament traits have been observed in a wide range of age groups, spanning adolescence (Heiman et al. 2004
), young adulthood (Ando et al. 2004
), and older adulthood (Heiman et al. 2003
; Stallings et al. 1996
). This study explored the biometric architecture of Cloninger’s personality system in a preadolescent sample. To our knowledge, it is also the first study to examine whether (J)TCI scales are measurement invariant with respect to sex. The pattern of heritability reported so often in other studies of temperament did not emerge. Among JTCI temperament traits, only Harm Avoidance was moderately influenced by genetic factors in this pre-adolescent sample of twins. Furthermore, strict factorial invariance was tenable only for Harm Avoidance.
Girls had higher scores than boys on the latent Harm Avoidance factor. This is an interesting finding, given that sex differences in internalizing problems largely emerge after puberty (Achenbach & Rescorla, 2006
). The present results suggest that elevated behavioral inhibition in girls may represent a latent liability for internalizing psychopathology that does not manifest itself until adolescence. However, not all studies indicate that girls score higher on Harm Avoidance (Lyoo et al. 2004
; Luby et al. 1999
). In a cross-sectional study of children aged 11–18, the sex difference in Harm Avoidance was most pronounced in late adolescence (Heiman et al. 2004
). In adults, women consistently outscore men on Harm Avoidance (Miettunen et al. 2007
). Females may compensate for this by having more mature character development (e.g. higher Cooperativeness) that protects them from internalizing problems, at least in preadolescence. There was some evidence that girls scored higher than boys on the character dimensions (both on Cooperativeness and Self-directedness), which might reflect their greater social and emotional maturity. Unfortunately, neither Cooperativeness nor Self-directedness was measurement invariant, rendering it difficult to assess mean sex differences in these constructs.
Factorial invariance was only partially supported for Novelty Seeking. Boys had higher scores on the Exploratory Excitability facet, which was disproportionately high relative to their scores on the other Novelty Seeking subscales; the mean of the latent factor did not significantly differ across sex. Measurement invariance was rejected in the cases of Reward Dependence and Persistence, but the appalling internal consistency likely played a role in these failures. In general, Reward Dependence shows the most robust sex difference on the TCI, with an average effect size of 0.63 in favor of women (Miettunen et al. 2007
). In fact, we are unaware of a single study that has failed to detect a significant sex difference in JTCI Reward Dependence. However, the present study casts doubt on the comparability of this construct across sex, and underscores the need to establish unbiasedness before jumping to conclusions about mean differences. Gender bias may especially plague the Sentimentality subscale of Reward Dependence, as the items appear to reflect feminine stereotypes. It is not inconceivable that males would be more hesitant to admit to certain items (e.g. “I usually cry when I see sad movies”) due to gender role considerations.
Among the two character traits examined, only Self-directedness was significantly heritable. This fits well with the consensus that genetic influences on self-esteem are substantial during childhood (Neiss et al. 2002
). In female preadolescent twins, for example, Hur et al. (1998)
found that genetic, but not shared environmental, factors were significant for several domains of self-concept. Self-directedness, in the present study, similarly failed to show evidence of shared environmental influence. On the other hand, there was evidence of shared environmental influences on Cooperativeness. This is not surprising, as Altruism, which is a closely related characteristic, is probably also influenced by shared environmental factors (Koenig et al. 2007). Indeed, Ando et al. (2004)
found that shared environmental factors explained a significant proportion (0.27) of the variance in the Empathy subscale of Cooperativeness.
These findings partially support Cloninger’s (1993)
speculation that character is shaped by genes as well as between-family environments. More specifically, our results suggest thatCooperativeness and Self-directedness have a different genetic/environmental architecture in childhood (particularly for girls). It appears that children’s self-concepts of personal effectiveness are largely heritable, whereas children’s orientation towards others (e.g. social acceptance and helpfulness) is more influenced by the family-wide environment. The young age and ethnic diversity of our sample may have contributed to this finding. Children might be particularly sensitive to religious and parental views concerning social tolerance. Also, mean differences in Cooperativeness between ethnic groups could account for some of the shared environmental variance. Given the purported influence of sociocultural learning on character development, the multicultural composition of our sample is not inappropriate.
An important caveat is that the constructs of Self-directedness and Cooperativeness may have different meaning in boys and girls. We decomposed the variance in each sex separately because the latent factors were not comparable across sex. Familial aggregation of character was unusually high in both sexes (50 – 70%). This is doubtlessly a by-product of our latent variable approach, in which the subscale-specific measurement error was effectively removed from the common variance of each trait.
Phenotypic correlations between JTCI scales departed slightly from the adult pattern. There are modest correlations between Harm Avoidance and Novelty Seeking on the adult TCI (see Miettunen et al. 2008
). In the present study, however, there was no association between Harm Avoidance (HA) and Novelty Seeking (NS). Furthermore, the remaining JTCI scales (i.e. Reward Dependence, Persistence, Self-directedness, and Cooperativeness) comprised a mutually positive cluster of traits that was negatively correlated with both HA and NS. This correlation structure has appeared in other investigations of the JTCI (Lyoo et al. 2004
; Copeland et al. 2004
), suggesting that elevated HA and NS scores independently predict poor character development in children.
A major limitation to the generalizability of our results is the unusual way in which the questionnaire was administered. Since items were orally dictated to the subjects who, in turn, directly verbalized their responses to the tester, there may have been attenuation in reliability and/or increases in social desirability. However, the problems with the JTCI may be intrinsic to this age group. It is likely that children aged 9–10 are not reliable informants, and that the JTCI is a poor instrument for measuring personality in middle childhood. The preliminary work by Luby et al. (1999)
suggested that the JTCI is appropriate for children aged 9–13, but this is somewhat misleading, as older children were oversampled (nearly half were aged 13).
Persistence and Reward Dependence, in particular, suffered from an unacceptably low internal consistency. This is an inconvenience that often plagues Persistence on account of its small number of items. For example, Schmeck et al. (2001)
obtained reliability coefficients of .48 and .51 for Persistence and Reward Dependence, respectively, within a sample of adolescents. It is possible that the reliability of these scales may improve with age. Indeed, reliability data was available for 400 participants from the present study who were administered the JTCI again at age 14. Cronbach’s alpha for Persistence and Reward Dependence was higher during adolescence, with coefficients of .53 and .63, respectively.
In general, poor measurement properties deflate the magnitude of twin covariance. Since the relative effects of A and C are likely to be underestimated when measurement error is not adequately addressed, we employed a common pathway model as a starting base for the model-fitting procedure. Unfortunately, in all cases, a single latent factor rendered a poor fit when compared to a saturated model. This suggests the possibility that the JTCI scales may not be unidimensional in this age group. A revision of the JTCI may be necessary to improve its psychometric qualities.
On top of this, our power to resolve between the various sources of twin covariance (i.e. A and C) may have been limited due to our relatively small sample size. For example, the intraclass correlations were sufficiently similar across MZ and DZ twins to suggest the presence of shared environmental (C) effects on Cooperativeness. Yet the power of detecting significant C effects on the latent trait of Cooperativeness was only .38 in boys. Nearly thrice the current sample size (N = 1719 pairs) would be required to achieve a power of .80. Furthermore, our estimates of A and C do not precisely capture the broad influences that they purport to measure. For example, the effect of C might be masked by genetic non-additivity. In the absence of alternative designs (e.g. measured genotypes or twins separated at birth), it is impossible to accurately state the mechanisms involved.
Other studies have not been hampered by small sample sizes, and have often obtained results that sharply differ from the present estimates. In fact, one large study exploited a more powerful design (i.e. extended sibships of twins) to detect the effects of genetic non-additivity on TCI traits (Keller et al. 2005
). In contrast to our finding of limited familial influences (and, in fact, modest C effects) on Novelty seeking, they found evidence of non-additive genetic variation in Novelty Seeking as well as Reward Dependence and Persistence. However, the disparity in results cannot simply be attributed to differences in design, as the subjects used by Keller et al. (2005)
were older (i.e. post-adolescent).
In the present study, the absence of familial influences on Persistence and Reward Dependence can easily be attributed to poor measurement properties, but the lack of heritability for Novelty Seeking is less explicable. Cronbach’s alpha for Novelty Seeking was approximately .60, which although sub-optimal, is comparable to the .66 coefficient obtained by Heiman et al. (2004)
in twins aged 11–18. The heritability estimate in the latter group was 36%, and was obtained via self-report. The discrepancy between the present results and those of Heiman et al. (2004)
is perhaps linked to the fact that Novelty Seeking scores are much lower in preadolescents. It is possible that the genetic predisposition for Novelty Seeking does not fully emerge until adolescence, when risk-taking behavior becomes more normative. Alternatively, the present subjects may have responded to the items differently due to the peculiar method in which the JTCI was administered.
Despite these limitations, these results are the first to demonstrate that Cloninger’s Self-directedness scale is heritable in both males and females during childhood. Deficient levels of Self-directedness may serve as genetically-mediated risk factors for various types of child psychopathology. Of the four temperament traits, only Harm Avoidance was found to be heritable. This is in contrast to studies of older children and adults, in which genetic influences on Novelty Seeking have consistently been found. It remains to be seen how these characteristics and their genetic and environmental architecture develop over time in future assessments within this longitudinal project.