In agreement with earlier CAH studies Berenbaum et al. Danish — oral, written and spelling average f. Parental educational attainments were coded as categorical variables for the highest obtained education by December 31, Additionally, twin studies with siblings as a control group for the psychosocial environment also failed to find evidence for socialization effects Heil et al. However, excluding twins with known MZ status does only change the point estimates marginally. Overall, male twins and singletons showed significantly higher ninth-grade test scores in mathematics than females Table 3 ; however, the effect sizes were small adjusted difference.
However, all analyses were repeated including birth weight results not shownand the results were similar.
Sex-typed play in opposite-sex twins.