Table 1 Characteristics of the study populations

<45 dB

45–55 dB

> = 55 dB

<45 dB

45–55 dB

> = 55 dB

N (%)

202 (10.4)

620 (32.1)

1112 (57.5)

N (%)

158 (11.4)

617 (44.6)

587 (44.0)

Mean fraction of inattention score (SD)

.17 (.15)

.19 (.14)

.19 (.15)

Mean fraction of inattention score (SD)

.19 (.16)

.18 (.14)

.20 (.16)

% Boys

47.5

49.4

49.9

% Boys

52.5

50.4

49.8

Age, months (SD)

97.3 (1.2)

97.3 (1.3)

97.5 (1.4)

Age, months (SD)

97.3 (1.2)

97.4 (1.4)

97.5 (1.5)

Income, birth (SD)^a

825,843

824,736

757,927

Average 5-y income (SD)^a

1,052,194

1,047,947

920,016

(585473)

(685930)

(495249)

(585321)

(519580)

(542098)

Mother’s education

Mother’s education

  > 4 years univ./college

35.6

36.3

37.6

  > 4 years univ./college

40.5

42.0

41.5

  ≤ 4 years univ./college

52.5

48.2

50.4

  ≤ 4 years univ./college

47.5

45.7

44.3

 High school

11.9

15.5

12.1

 High school

12.0

12.3

14.1

Ethnicity: % western^b

96.5

93.1

93.5

Ethnicity: % western^b

92.4

94.3

88.0

Premature^c, %

4.5

4.2

4.3

Premature^c, %

8.2

4.1

3.9

Low birth weight^d, %

1.5

2.9

3.0

Low birth weight^d, %

3.2

2.9

4.3

Urbanity

Urbanity, birth

 City center

9.9

8.6

34.8

 City center

 Between

19.3

27.4

30.0

 Between

 Outskirts

70.8

64.0

35.3

 Outskirts

Urbanity,5-y average (SD)

Urbanity, 5-y average (SD)

2.77 (.48)

2.77 (.43)

2.40 (.72)

Maternal alcohol, Pregnancy^e, % yes

7.9

7.4

7.0

Maternal alcohol, Pregnancy^e, % yes

7.0

10.2

9.5

Maternal smoking, Pregnancy^f, % yes

3.5

3.1

4.5

Maternal smoking, Pregnancy^f, % yes

3.8

3.4

5.1

Sleep duration at age 8

Sleep duration at age 8

  > 10 h

  > 10 h

20.9

14.3

18.2

 10 h

 10 h

62.0

66.6

63.4

  < 10 h

  < 10 h

17.1

19.1

18.4