Table 2.

Background Information of the Study Population

	First sibling			Second sibling
	n	Maternal smoking exposurea, %	Child’s psychiatric diagnosis, %	n	Maternal smoking exposurea, %	Child’s psychiatric diagnosis, %	Total, n
All children	150 168	15.0	18.7	150 168	13.6	18.7	300 336
Maternal age
<20	7256	38.1	27.7	1149	41.9	33.8	8405
20–34	135 999	13.9	17.8	130 190	13.8	18.6	266 189
35 or more	6913	11.8	19.3	18 829	10.3	18.7	25 742
Marital status, single
No	138 948	13.1	14.4	142 499	12.4	18.3	281 447
Yes	11 220	29.4	19.7	7669	29.3	25.0	18 889
Parity
0	110 669	14.6	18.0	0	0.0	0.0	110 684
1	23 657	15.2	19.0	111 281	12.8	18.3	134 938
2–3	11 457	17.3	20.3	33 582	16.3	20.1	45 039
4 or more	2467	7.0	18.2	5017	12.4	18.9	7484
Unknown	1918	15.9	18.4	288	29.2	23.8	2191
Mother’s psychiatric diagnosis
No	140 247	15.3	17.3	140 247	12.5	17.7	280 494
Yes	9921	30.1	33.5	9921	29.2	33.2	19 842
Sibling’s psychiatric diagnosis
No	122 112	17.3	17.3	127 884	13.87	12.0	249 996
Yes	28 056	27.6	31.2	22 284	20.7	24.8	50 340
Sex
Male	76 433	15.0	17.6	76 221	13.5	18.6	152 654
Female	73 735	15.0	19.1	73 947	13.6	18.9	147 682
Birth weight
<1500	376	25.5	34.6	368	25.6	43.5	744
1500–2499	3219	15.5	22.1	2052	27.3	26.9	5271
2500–3999	118 925	15.7	18.4	110 226	14.9	18.9	229 151
4000 or more	26 388	10.4	17.4	36 793	8.5	17.5	63 181
Unknown	1260	5.9	18.9	729	16.7	22.2	1989
Gestational age, wk
23–27	102	15.6	43.1	130	26.6	51.5	232
28–31	369	20.6	30.6	390	23.4	34.4	759
32–36	5325	17.2	19.8	4147	18.4	21.4	9472
37 or more	142 743	14.9	18.3	144 467	13.4	18.6	287 210
Unknown	1629	20.5	19.4	1034	16.0	22.4	2663
1-min Apgar score
0–3	1097	16.1	22.6	653	18.0	26.2	1750
4–6	4111	15.1	19.2	2584	15.2	20.6	6695
7–10	143 605	15.0	18.3	146 017	13.5	18.6	289 622
Unknown	1355	20.0	19.0	914	22.5	22.9	2269

^aexcluding unknown smoking.