Table 2.

Characteristics of Study Population, Kaiser Permanente Northern California Childhood Autism Perinatal Study, 1995 – 1999

	Cases (N = 407) n (%)	Controls (N = 2075) n (%)
Female	74 (18.2)	385 (18.5)
Male	333 (81.8)	1690 (81.4)
Plurality
Singleton	383 (94.1)	2010 (96.8)
Multiple (twin or triplet)	24 (5.9)	57 (2.7)
Maternal Age (years)
<20	6 (1.5)	85 (4.1)
20–24	45 (11.0)	298 (14.4)
25–29	100 (24.6)	584 (28.1)
30–34	137 (33.7)	660 (31.8)
35–39	99 (24.3)	374 (18.0)
≥40	20 (4.9)	74 (3.6)
Maternal Education
<High school	21 (5.2)	206 (9.9)
High school graduate	79 (19.4)	597 (28.8)
College	223 (54.8)	983 (47.4)
Post-graduate	81 (19.9)	256 (12.3)
Unknown	3 (0.7)	25 (1.2)
Maternal Race/Ethnicity
White, non-Hispanic	210 (51.6)	936 (45.1)
White, Hispanic	66 (16.2)	471 (22.7)
Black	35 (8.6)	186 (8.9)
Asian	42 (10.3)	215 (10.4)
Other	54 (13.3)	267 (12.9)
Gestational Age
< 37 Weeks	42 (10.3)	134 (6.5)
≥37 Weeks	365 (89.7)	1941 (93.5)
Birth Weight
< 2500 grams	28 (6.9)	101 (4.9)
≥2500 grams	379 (93.1)	1974 (95.1)
Parity
Primiparous	172 (42.3)	891 (42.9)
Multiparous	234 (57.5)	1176 (56.7)
Missing	1 (0.2)	8(0.4)
Birth Year
1995	119 (29.2)	607 (29.3)
1996	106 (26.0)	550 (26.5)
1997	78 (19.2)	387 (18.7)
1998	77 (18.9)	396 (19.1)
1999	27 (6.6)	135 (6.5)