Table 1.

Sample characteristics, by age and group

	HRA+	HRA−	LRC	c p (3-group)
Sex (% female)	30.0 n = 30	53.5 n = 71	44.9 n = 69	.09
Race/ethnicity (% White)	83.3 n = 30	95.7 n = 71	88.4 n = 69	.08
a Household income	7.08 (2.02) n = 24	7.69 (0.91) n = 67	7.52 (1.38) n = 58	.79
b Mother’s level of education	5.04 (1.72) n = 25	5.74 (1.65) n = 68	6.65 (1.22) n = 62	.0002***
Actual age at visits (month)
6 months	5.91 (0.43) n = 22	5.96 (0.28) n = 50	5.97 (0.36) n = 61	.79
12 months	11.93 (0.45) n = 30	11.94 (0.38) n = 67	11.87 (0.42) n = 67	.54
18 months	18.12 (0.78) n = 25	17.91 (0.42) n = 67	18.01 (0.27) n = 67	.11
24 months	24.16 (0.55) n = 25	24.03 (0.55) n = 61	24.10 (0.56) n = 63	.60
36 months	36.09 (0.68) n = 22	36.57 (1.50) n = 51	36.33 (0.64) n = 54	.20

Data are reported as group means with standard deviations in parentheses

^aIncome was reported on an 8-point scale: (1) less than $15,000, (2) $15,000–$25,000, (3) $25,000–$35,000, (4) $35,000–$45,000, (5) $45,000–$55,000, (6) $55,000–$65,000, (7) $65,000–$75,000, (8) more than $75,000

^bEducation was reported as the highest level attained on a 9-point scale: (1) some high school, (2) high school graduate, (3) some college, (4) community college/two-year degree, (5) four-year college degree, (6) some graduate school, (7) master’s degree, (8) doctoral degree, (9) professional degree

^cFisher’s exact tests were used to determine p values for group differences in sex and race/ethnicity. Kruskal-Wallis tests were used to determine p values for group differences in income and maternal education. One-way ANOVA tests were used to determine p values for group differences in age

***p < .001