TABLE 1.
Demographic characteristics of the increased likelihood (IL) sample.
| Measure | IL-N | IL-ASD | Statistic | p |
| Sex | 75 boys: 52 girls | 32 boys: 19 girls | X2 = 0.21 | 0.65 |
| Child age (months) | Mean (±SD) | Mean (±SD) | Statistic | P |
| Age at 6-month IBQ | 6.45 (0.77) | 6.60 (1.07) | Z = –0.14 | 0.89 |
| Age at 12-month IBQ | 12.46 (0.91) | 12.50 (0.70) | Z = –1.22 | 0.22 |
| Age at 24-month TBAQ-R | 24.43 (0.67) | 24.25 (0.60) | Z = –1.37 | 0.17 |
| Age at 3-year Ax | 38.08 (2.32) | 37.98 (2.73) | Z = –1.21 | 0.23 |
| Age at CBCL/5-year Ax | 65.47 (5.06) | 64.23 (4.38) | Z = –0.59 | 0.56 |
| Parent age (years) | Mean (±SD) | Mean (±SD) | Statistic | p |
| Mother age at child birth | 34.17 (4.29) | 34.63 (4.48) | Z = –0.58 | 0.56 |
| Father age at child birth | 36.70 (4.73) | 37.49 (4.73) | Z = –0.53 | 0.59 |
| Measure | % | % | Statistic | P |
| Family SES | ||||
| <20 | 2 | 0 | X2 = 0.36 | 0.36 |
| 21 to =35 | 16 | 14 | ||
| 36 to =50 | 35 | 27 | ||
| 51 to =127 IL–66 | 47 | 59 | ||
| Mothers’ ethnicity | ||||
| Caucasian | 60.62 | 66.67 | X2 = 5.16 | 0.64 |
| African | 1.57 | 3.92 | ||
| Aboriginal | 1.57 | 0 | ||
| Asian | 3.94 | 3.92 | ||
| East Indian | 1.58 | 1.96 | ||
| Southeast Asian | 3.15 | 0 | ||
| Mixed Heritage | 3.15 | 0 | ||
| Unknown | 24.42 | 23.53 | ||
| Fathers’ ethnicity | ||||
| Caucasian | 62.99 | 68.63 | X2 = 7.93 | 0.44 |
| African | 0 | 3.92 | ||
| Aboriginal | 1.57 | 0 | ||
| Asian | 3.94 | 1.96 | ||
| East Indian | 3.15 | 1.96 | ||
| Hispanic | 0.80 | 0 | ||
| Southeast Asian | 1.57 | 0 | ||
| Mixed Heritage | 1.57 | 1.96 | ||
| Unknown | 24.41 | 21.57 |
Group (ASD or Non-ASD) for statistical comparisons used blind diagnostic assessment at age 5. Socioeconomic status (SES) is based on the Hollingshead Four-Factor Index, a composite score comprised of education, occupation, sex, and marital status (Hollingshead, 1975). Hollingshead Index raw scores range from 8 to 66, with higher scores reflecting higher SES.
Ax, Assessment; IBQ, Infant Behavior Questionnaire; CBCL, Child Behavior Checklist; IL-ASD, Increased Likelihood sibling with ASD; IL-N, Increased Likelihood Sibling without ASD; SD, standard deviation; TBAQ-R, Toddler Behavior Assessment Questionnaire-Revised.