Table 1 Sample characteristics of children with autism symptom questionnaire data from single and multiple incidence families in IAN
|  | Single incidence families | Multiple incidence families | Χ 2, t(p) |
|---|---|---|---|
Number of families | 2262 | 315 | Â |
 Female ASD-containing (N, %) | 334 (14.8 %)a | 125 (39.7 %)b | Χ 2(1) = 117.3 (p < .001) |
 Male-only (N, %) | 1928 (85.2 %)a | 190 (60.3 %)b |  |
Number of children | 4764 | 751 | Â |
 ASD (N, %) | 2262 (48.8 %)a | 596 (80.6 %)b | Χ 2(2) = 261.1 (p < .001) |
 Non-ASD (N, %) | 2097 (45.2 %)a | 121 (16.4 %)b |  |
 Non-ASD with HLDAS | 280 (6.0 %)a | 22 (3.0 %)b | |
Age (M, SD, range) | 8.7 (3.8, 4–18) | 8.8 (3.6, 4–18) | t(5513) = −0.6 (p = .522) |
Female siblings (N, %) | 1602 | 221 | Â |
 ASD (N, %) | 333 (20.8 %)a | 141 (63.8 %)b | Χ 2(2) = 187.7 (p < .001) |
 Non-ASD with HLDAS (N, %) | 118 (7.4 %) | 11 (5.0 %) |  |
 Non-ASD (N, %) | 1151 (71.8 %)a | 69 (31.2 %)b |  |
Race/ethnicity | |||
 White non-Hispanic | 4248 (89.2 %) | 684 (91.1 %) | Χ 2(1) = 2.5 (p = .114) |
 Other or unknown | 516 (10.8 %) | 67 (8.9 %) |  |
SCQ total raw (M, SD) | 12.4 (11.4) | 17.5 (10.3) | t(5513) = −11.54 (p < .001) |
SRS total T score (M, SD) | 64.7 (23.8) | 77.1 (21.2) | t(5513) = −13.47 (p < .001) |
DSM-IV-TR (N, %) | |||
 Autistic disorder | 950 (42.0 %) | 239 (40.1 %) | Χ 2(2) = 10.7 (p = .005) |
 PDD NOS | 963 (42.6 %) | 232 (38.9 %) | |
 Asperger’s disorder | 349 (15.4 %)a | 125 (21.0 %)b | |