Table 2.
Twin correlations and cross-twin cross-trait correlations
| Trait | MZ twin correlation | N(pairs) | DZ twin correlation | N(pairs) |
| ADHD combined | .86 | 2013 | .48 | 3567 |
| Inattentiveness | .79 | 2012 | .37 | 3568 |
| Hyp-imp | .88 | 2013 | .48 | 3565 |
| Reading | .77 | 1861 | .46 | 3186 |
| Reading comprehension | .65 | 1862 | .41 | 3220 |
| Word decoding | .77 | 1968 | .42 | 3363 |
| Trait | MZ cross-twin cross-trait correlation | N(pairs) | DZ cross-twin cross-trait correlation | N(pairs) |
| ADHD combined t1—reading t2 | −.20 | 1670 | −.11 | 2895 |
| Inattentiveness t1—reading t2 | −.20 | 1669 | −.07 | 2897 |
| Hyp-imp t1—reading t2 | −.17 | 1667 | −.14 | 2897 |
| Inattentiveness t1—hyp-imp t2 | .53 | 2012 | .32 | 3565 |
| Inattentiveness t1—reading comprehension t2 | −.19 | 1666 | −.05 | 2900 |
| Inattentiveness t1—word decoding t2 | −.13 | 1734 | −.05 | 3009 |
| Hyp-imp t1—reading comprehension t2 | −.09 | 1735 | −.10 | 3006 |
| Hyp-imp t1—word decoding t2 | −.15 | 1670 | −.15 | 2894 |
| Word decoding t1—reading comprehension t2 | .42 | 1868 | .28 | 3218 |
Note. MZ = monozygotic; DZ = dizygotic twins