Table 1.

Sample Characteristics

	Sibs-ASD	Sibs-TD	Groups Differ
Gender (% Male)	85.7%	51.5%	*
Race (% Caucasian)	33.3%	69.7%	*
Maternal Education
High school/some college	11.8%	16.7%
College degree	64.7%	53.3%
Graduate degree	23.5%	30.0%
Family Income
Less than $50K annually	25.0%	10.0%
$50–$100K annually	12.5%	30.0%
More than $100K annually	62.5%	60.0%
6 month time point
Chronological age	6.5 (.9)	6.0 (.4)
Verbal Mental age	5.6 (.8)	5.1 (.8)
Nonverbal Mental age	5.6 (.7)	6.6 (1.2)	+
12 month time point
Chronological age	12.4 (.6)	12.6 (.6)
Verbal Mental age	10.5 (2.2)	10.4 (2.2)
Nonverbal Mental age	12.6 (1.8)	12.5 (1.9)
18 month time point
Chronological age	18.4 (.4)	18.6 (.6)
Verbal Mental age	14.9 (5.1)	17.6 (3.0)
Nonverbal Mental age	17.6 (2.1)	18.8 (2.1)
24 month time point
Chronological age	24.4 (.6)	24.6 (.6)
Verbal Mental age	20.5 (5.6)	25.6 (2.8)	*
Nonverbal Mental age	20.5 (1.9)	25.8 (4.0)	**
ASD Severity Rating	4.8 (2.2)	1.3 (.5)	**
36 month time point
Chronological age	37.8 (4.0)	36.6 (.5)	**
Verbal Mental age	33.8 (5.8)	38.6 (3.9)	*
Nonverbal Mental age	33.6 (7.4)	40.7 (4.3)	*
ASD Severity Rating	6.1 (2.0)	1.8 (1.4)	**

Assessment related data are presented as Mean (Standard Deviation). Chronological age and mental age data are reported in months. Chi-squared analyses and T-tests indicate that the groups differ as represented by the following symbols:

⁺p < .05;

^*p < .01;

^**p < .001.