Multiple regression analysis of reading performance data from twin                     pairs with reading difficulties and nontwin siblings: the augmented model.
The augmented multiple regression model for the analysis of data from selected                    twin pairs was extended to facilitate analyses of data from twin pairs and                    nontwin siblings. Fitting this extended model to data from both selected twin                    pairs and siblings yields direct estimates of heritability (h2) and                    the difference between environmental influences shared by members of twin pairs                    and those of sib or twin-sib pairs (i.e., c2(t)                    - c2 (s)). When this model was fitted to reading                    performance data from 293 monozygotic and 436 dizygotic pairs selected for                    reading difficulties, and 291 of their nontwin siblings, h2 = .48                    ± .22, p = .03, and c2 (t) -                    c2 (s) = .22 ± .12, p = .06. Although the test                    for differential shared environmental influences is only marginally significant,                    the results of this analysis suggest that environmental influences on reading                    performance that are shared by members of twin pairs (.36) may be substantially                    greater than those for less contemporaneous twin-sibling pairs                (.14).
Institute for Behavioral Genetics, University of Colorado, Boulder, CO 80309, USA. Sally.Wadsworth@Colorado.edu
Sally J
SJ
Wadsworth
Richard K
RK
Olson
Erik G
EG
Willcutt
John C
JC
DeFries
D000293:Adolescent; D003120:Colorado; D005260:Female; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D011932:Reading; D012044:Regression Analysis; D035781:Siblings; D014429:Twins, Dizygotic / Q000193:education* / Q000235:genetics; D014430:Twins, Monozygotic / Q000193:education* / Q000235:genetics; D055815:Young Adult