Table 1 Associations between environmental risk factors and IQ scores

Gender

Boy (n = 23)

56.4 (7.3)

67.9 (11.5)

11.5 (8.7)

<0.001*

Girl (n = 13)

58.0 (9.5)

60.2 (12.5)

2.2 (9.0)

0.406

p ^b

0.515

0.081

0.005*

Test interval (median = 16 month)

≤ Median (n = 19)

57.6 (6.3)

65.5 (10.6)

7.9 (9.3)

0.005*

> Median (n = 17)

56.2 (9.8)

64.6 (14.3)

8.4 (10.7)

0.002*

p ^b

0.827

0.827

0.975

Low maternal education level

Yes (n = 14)

56.3 (8.5)

68.6 (11.3)

12.4 (9.0)

<0.001*

No (n = 22)

57.4 (7.9)

62.9 (12.6)

5.5 (9.6)

0.014*

p ^b

0.708

0.211

0.047*

Low father’s education level

Yes (n = 10)

57.0 (8.5)

67.5 (13.9)

10.5 (9.8)

0.008*

No (n = 26)

57.0 (8.1)

64.2 (11.8)

7.2 (9.9)

0.001*

p ^b

0.887

0.621

0.367

Low income

Yes (n = 4)

55.0 (8.8)

66.8 (15.5)

11.8 (7.3)

0.048*

No (n = 32)

57.2 (8.1)

64.9 (12.1)

7.7 (10.1)

0.001*

p ^b

0.667

0.743

0.449

Single-parent family

Yes (n = 5)

48.8 (5.2)

58.2 (14.1)

9.4 (10.6)

0.104

No (n = 31)

58.3 (7.7)

66.2 (11.9)

7.9 (9.9)

<0.001*

p ^b

0.016*

0.234

0.819

Grand parenting

Yes (n = 6)

56.8 (9.7)

67.7 (18.2)

10.8 (9.5)

0.039*

No (n = 30)

57.0 (7.9)

64.6 (11.1)

7.6 (10.0)

<0.001*

p ^b

0.983

0.832

0.580