Table II.
Phenotypic correlations for reading achievement and reading disability.
| Familial Relationship | Phenotypic Pearson correlation for reading achievement (95% confidence interval) |
Phenotypic tetrachoric correlation for reading disability (95% confidence interval) |
|---|---|---|
| Spouses | 0.255 (0.215, 0.294) |
0.093 (−0.081, 0.262) |
| MZ twins | 0.743 (0.723, 0.763) |
0.858 (0.791, 0.925) |
| DZ twins & bio sibs | 0.392 (0.339, 0.441) |
0.433 (0.405, 0.618) |
| Unrelated sibs (in adoptive families) |
0.058 (−0.038, 0.152) |
−0.061 (−0.465, 0.334) |
| Biological offspring with mother |
0.338 (0.307, 0.368) |
0.301 (0.194, 0.408) |
| Biological offspring with father |
0.36 (0.330, 0.395) |
0.419 (0.326, 0.511) |
| Adopted offspring with mother |
0.072 (−0.003, 0.146) |
0.223a (−0.093, 0.502) |
| Adopted offspring with father |
0.088 (0.009, 0.166) |
a
Because only one parent per adoptive family had known reading-disability status, only one value was computed for the adoptive parent-child tetrachoric correlation, ignoring sex of parent.