Temperament was assessed through separate mother and father ratings
in a sample of 354 German mono- and dizygotic twin pairs aged 2 to 14 years.
We administered the EAS Temperament Survey (Buss & Plomin, 1984) measuring
Emotionality, Activity, Sociability, and Shyness to investigate the usefulness
of the 20-item inventory for behavior genetic studies of early developing
personality traits in children. Most of the studies that report zero or
even negative correlations for dizygotic twins in parental ratings assessed
temperament in very young children only. The present study covered a larger
age range to examine whether this pattern of results was also found in
parental ratings of older children when the same inventory was used.
Our findings clearly demonstrate that similarities of dizygotic twins were substantially less than half the MZ twin correlations. For all EAS dimensions except Emotionality, DZ twin correlations were close to zero or negative Hardly any systematic correspondence emerged between age and twin similarity. The design of our study made it possible to analyze contrast effects, which might be responsible for DZ twin dissimilarity, within and across raters. We found evidence that contrast effects were not only observed in separate mother or father ratings but were also found when cross-correlations were analyzed.
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