Table 3.

Comparisons of study samples and non-participants

	Pregnancy	sample		Postnatal	sample
	Study sample	Non-participants	p-value	Study sample	Non-participants	p-value
Average 5-y road traffic noise (SD), n				54.1 (7.4), n = 1384	55.1 (7.6), n = 4834	<.0001
Road traffic noise at age 8 (SD), n				53.1 (7.8), n = 1384	53.9 (8.2), n = 5484	.001
Road traffic noise, pregnancy (SD), n	55.8 (8.3), n = 1934	56.6 (8.4), n = 6425	.0001
Average 5-y income (SD), n				992,139 (540759), n = 1384	901,693 (580480) n = 7579	<.0001
Income at age 8 (SD), n				1,046,052 (621477), n = 1384	948,394 (678449) n = 7719	<.0001
Income, pregnancy (SD), n	786,438 (573046), n = 1934	767,439 (587234), n = 9688	.19
Mother’s education, n	n = 1934	n = 10,036		n = 1384	n = 10,586
> 4 years univ./college	37.0	33.5	<.001	41.6	33.1	<.001
≤ 4 years univ./college	49.9	47.1		45.3	47.8
High school	13.1	19.4		13.1	19.1
Ethnicity, % western, n	93.7, n = 1934	86.6, n = 10,148	<.001	91.3, n = 1384	87.3, n = 10,698	<.001
Gender, % boys, n	49.5, n = 1934	50.9, n = 10,206	.26	50.4, n = 1384	50.7, n = 10,756	.81
Maternal smoking, pregnancy, % yes	3.9, n = 1934	4.8n n = 8871	.12	4.2, n = 1384	4.7, n = 9421	.44
Maternal alcohol consumption, pregnancy, % yes	7.2, n = 1934	7.3, n = 7278	.98	9.5, n = 1384	6.9, n = 7828	<.001
% birth weight < 2500 g, n	2.8, n = 1934	3.2, n = 10,202	.33	3.5, n = 1384	3.1, n = 10,752	.37
% premature, n	4.3, n = 1934	4.7, n = 10,192	.39	4.5, n = 1384	4.7, n = 10,742	.73