Table 1.
Sample characteristics.
| Total sample (all ages/children/adults) | Sample for within-pair difference analyses | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Twins discordant for ADHD diagnosis (all ages/children/adults) | Twins differing for ADHD symptoms (all ages/children/adults) | |||||||||
| MZ | DZ | MZ | DZ | |||||||
| Pairs (n) | 191/127/64 | 14/12/2 | 35/30/5 | 44/33/11 | 61/44/17 | |||||
| Age | ||||||||||
| Mean | 16.62/13.11/23.59 | 14.14/12.33/25.00 | 13.51/12.47/19.80 | 16.02/13.48/23.64 | 15.33/12.73/22.06 | |||||
| SD | 5.92/2.55/4.29 | 5.16/2.41/3.46 | 3.44/2.21/2.78 | 5.41/4.82/3.98 | 5.01/2.37/3.56 | |||||
| Range | 8–33/8–17/18–33 | 9–28/9–17/22–28 | 8–25/8–16/18–25 | 8–28/8–17/18–28 | 8–31/8–17/18–31 | |||||
| ADHD | Non-ADHD | ADHD twin | Co-twin | ADHD twin | Co-twin | Higher attention score | Lower attention score | Higher attention score | Lower attention score | |
|---|---|---|---|---|---|---|---|---|---|---|
| Subjects (n) | 103/92/11 | 279/162/117 | 14/12/2 | 14/12/2 | 35/30/5 | 35/30/5 | 44/33/11 | 44/33/11 | 61/44/17 | 61/44/17 |
| Sex, N subjects | ||||||||||
| Male | 64/61/3 | 137/89/48 | 16/16/0 | 22/19/3 | 21/18/3 | 56/50/6 | 32/23/9 | 37/27/10 | ||
| Female | 39/31/8 | 142/73/69 | 12/8/4 | 13/11/2 | 14/12/2 | 32/16/16 | 29/21/8 | 24/17/7 | ||
| NDD diagnosis, N subjects | ||||||||||
| ADHD | 103/92/11 | 0 | 14/12 /2 | 0 | 35/30/5 | 0 | 20/18/2 | 11/11/0 | 35/32/3 | 10/8/2 |
| ASD | 41/37/4 | 47/33/14 | 6/5/1 | 1/1/0 | 14/13/1 | 7/6/1 | 20/17/3 | 11/10/1 | 22/14/8 | 10/9/1 |
| ID | 10/10/0 | 10/7/3 | 2/2/0 | 0/0/0 | 1/1/0 | 0/0/0 | 7/7/0 | 3/3/0 | 2/0/2 | 2/2/0 |
| Other NDDs | 31/28/3 | 33/22/11 | 3/3/0 | 1/1/0 | 8/7/1 | 8/5/3 | 9/9/0 | 6/5/1 | 15/12/3 | 8/5/3 |
| Full-scale IQ | ||||||||||
| Mean | 94.42/94.37/94.82 | 100.83/100.49/101.30 | 99.15/98.27/104.00 | 100.86/100.67/102.00 | 97.74/97.72/97.80 | 100.29/101.60/92.40 | 90.19/86.90/99.45 | 94.95/92.34/102.55 | 97.38/98.61/94.00 | 102.77/104.68/97.82 |
| SD | 17.08/17.59/12.84 | 14.93/13.95/16.25 | 20.60/20.78/26.87 | 10.84/11.58/7.07 | 15.59/16.49/10.09 | 10.63/10.77/5.41 | 17.29/16.55/16.60 | 15.47/14.35/16.80 | 15.47/15.06/16.55 | 14.59/14.86/12.99 |
| Attention subscale score in CBCL/ABCL | ||||||||||
| Mean | NA/10.05/11.29 | NA/3.11/3.73 | NA/8.78/11.00 | NA/4.11/6.00 | NA/10.57/10.00 | NA/2.39/10.67 | NA/9.36/6.36 | NA/5.15/3.00 | NA/9.50/10.59 | NA/2.68/2.65 |
| SD | NA/3.87/3.59 | NA/3.42/4.60 | NA/2.95/2.83 | NA/2.32/2.83 | NA/3.99/2.65 | NA/2.85/12.66 | NA/3.63/4.11 | NA/4.00/3.63 | NA/4.22/5.96 | NA/3.18/3.43 |
ASD autism spectrum disorder, ADHD attention-deficit/hyperactivity disorder, ID intellectual disability, NDD neurodevelopmental disorder, MZ monozygotic twins, DZ dizygotic twins, CBCL the Child Behavior Checklist, ABCL Adult Behaviour Checklist.