. Author manuscript; available in PMC: 2009 Dec 3.

Published in final edited form as: J Intellect Disabil Res. 2008 May 29;52(12):1114–1128. doi: 10.1111/j.1365-2788.2008.01071.x

Table 1.

Demographics by intellectual status group at age six (n = 189)

	Group status
Variable	Intellectual disability (n = 74)	Typically developing (n = 115)	t or χ² value
Child Variables
Gender (% boys)	60.8	58.3	χ² = 0.04
Race (% Caucasian)	55.4	61.7	χ² = 0.51
Child health^†	3.27	3.79	t = 5.00^**
Mean Stanford Binet Mental Index (SD)	59.6 (14.4)	103.7 (12.0)	t = 22.74^**
Family variables
Maternal education (number of years)	14.5	15.9	t = 4.40^**
Mean maternal age (SD)	36.1 (6.5)	37.9 (5.9)	t = 1.42
Maternal employment (% employed)	65.2	52.7	χ² = 2.25
Maternal health^†	2.99	3.70	t = 1.86
Marital status (% married)	78.4	89.6	χ² = 1.80
Family income (% earning $50 000+)	46.8	67.0	t = 5.54^*

P < 0.05,

^**

P <0.001.

SD, standard deviation.

^†

Health scale: 1 = poor; 2 = fair; 3 = good; 4 = excellent.