Sj. Wadsworth et al., Stability of genetic and environmental influences on reading performance at 7 and 12 years of age in the Colorado Adoption Project, INT J BEHAV, 23(2), 1999, pp. 319-332
Results obtained from longitudinal studies suggest that individual differen
ces in reading performance are relatively stable over time. However, the ae
tiology of this stability has not been previously explored. In the current
study, the aetiology of longitudinal stability of reading performance betwe
en 7 and 12 years of age was assessed using data from adoptive (97 unrelate
d sibling pairs at age 7 and 73 pairs at age 12) and nonadoptive (106 relat
ed pairs at age 7 and 75 pairs at age 12) children tested in the Colorado A
doption Project. Results of a bivariate behavioural genetic analysis confir
med earlier findings of moderate genetic influence on individual difference
s in reading performance at both 7 and 12 years of age (h(2) = .49 and .37,
respectively). Moreover, about 70% of the observed stability (r = .61) bet
ween the two ages was due to common genetic influences. Of special interest
, no new heritable or shared environmental variation was manifested at age
12, suggesting that the same genetic and shared environmental influences we
re operating at both ages. In contrast, nonshared environmental influences
(e.g. instructional methods, teachers, peers, etc.) were responsible for ch
ange between 7 and 12 years of age, indicating the salience of such factors
for the development of reading performance between middle childhood and ad
olescence.