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Table 2 Potential confounding factors in relation to case-control status

From: Prenatal smoking exposure and neuropsychiatric comorbidity of ADHD: a finnish nationwide population-based cohort study

  

Cases

Controls

p

χ 2

Maternal age at birth

≤19 years

672 (6.7 %)

899 (2.4 %)

p < 0.001

603.69

20–29 years

5711 (56.5 %)

18,861 (51.1 %)

30–39 years

3475 (34.4 %)

16,143 (43.7 %)

≥40 years

254 (2.5 %)

1020 (2.8 %)

Paternal age at birtha

≤19 years

211 (2.2 %)

212 (0.6 %)

p < 0.001

330.41

20–29 years

4322 (44.2 %)

13,966 (38.2 %)

30–39 years

4358 (44.5 %)

18,892 (51.7 %)

≥40 years

896 (9.2 %)

3496 (9.6 %)

History of maternal psychopathology

Yes

2610 (25.8 %)

4340 (11.8 %)

p < 0.001

1154.75

No

7502 (74.2 %)

32,583 (88.3 %)

History of maternal substance abuse

Yes

685 (6.8 %)

747 (2.0 %)

p < 0.001

525.72

No

9427 (93.2 %)

36,176 (98.0 %)

History of paternal psychopathologya

Yes

2382 (24.3 %)

4597 (12.6 %)

p < 0.001

779.19

No

7405 (75.7 %)

31,969 (87.4 %)

Previous births

0

4683 (46.3 %)

15,077 (40.8 %)

p < 0.001

98.03

≥1

5429 (53.7 %)

21,846 (59.2 %)

Weight for gestational ageb

<-2 SD

569 (5.6 %)

1017 (2.8 %)

p < 0.001

189.09

-2 to +2 SD

9167 (91.0 %)

34,542 (93.8 %)

≥ + 2 SD

338 (3.4 %)

1257 (3.4 %)

Maternal SES

Upper white collar

861 (8.5 %)

5628 (17.7 %)

p < 0.001

593.56

Lower white collar

3986 (39.4 %)

6522 (15.2 %)

Blue collar

2439 (24.1 %)

16,528 (44.8 %)

Others

1959 (19.4 %)

5693 (15.4 %)

Missing

867 (8.6 %)

2552 (6.9 %)

Maternal immigrant status

Not born in Finland

223 (2.2 %)

542 (1.5 %)

p < 0.001

26.04

Born in Finland

9889 (97.8 %)

36,381 (98.5 %)

Paternal immigrant statusa

Not born in Finland

368 (3.8 %)

651 (1.8 %)

p < 0.001

136.41

Born in Finland

9419 (96.2 %)

35,915 (98.2 %)

Apgar score at 1 minc

<6

537 (5.3 %)

1376 (3.7 %)

p < 0.001

48.65

7–10

9565 (94.7 %)

35,504 (96.3 %)

Gestational age

≤32 weeks

224 (2.2 %)

245 (0.7 %)

p < 0.001

219.24

33–36 weeks

564 (5.6 %)

1408 (3.8 %)

37–41 weeks

8833 (87.6 %)

33,506 (91.0 %)

≥42 weeks

460 (4.6 %)

1677 (4.5 %)

  1. adata missing 682 subjects
  2. bdata missing: 107 subjects
  3. cdata missing 53 subjects