This article introduced methodology of human behavior genetics and twin study, especially multivariate genetic analysis, which was then applied to examine association between temperament and problem behaviors among children aged four to six years old. A questionnaire was mailed to 142 mothers of twins to obtain mother ratings of children's Effortful Control (EC), externalizing problems (EP), and internalizing problems (IP). Analysis of phenotypic correlations revealed that EP and IP had a positive correlation that was moderate (<i>r</i>=.55), and EC had a negative correlation with both EP (<i>r</i>=−.42) and IP (<i>r</i>=−.18). Multivariate genetic analysis revealed that the genetic influence that decreased EC also worked to increase both EP and IP, suggesting low EC may be a common genetic diathesis of EP and IP. Phenotypic correlation between EP and IP was explained by genetic (22.8%), shared environmental (53.4%), and non-shared environmental influence (23.8%). However, relatively low genetic contribution to the phenotypic correlation may be explained in terms of two counteracting influences: genetic influence on EC, which makes the correlation positive, and genetic influence unrelated to EC, which makes the correlation negative.
|Translated title of the contribution||Why Externalizing and Internalizing Problems Co-occur: Behavioral Genetic Analysis of Correlations|
|Number of pages||17|
|Publication status||Published - 2006|