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Table 1 Characteristics of the study populations

From: Road traffic noise and children’s inattention

Pregnancy sample Postnatal sample (5-year data example)
  <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: % westernb 96.5 93.1 93.5 Ethnicity: % westernb 92.4 94.3 88.0
Prematurec, % 4.5 4.2 4.3 Prematurec, % 8.2 4.1 3.9
Low birth weightd, % 1.5 2.9 3.0 Low birth weightd, % 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, Pregnancye, % yes 7.9 7.4 7.0 Maternal alcohol, Pregnancye, % yes 7.0 10.2 9.5
Maternal smoking, Pregnancyf, % yes 3.5 3.1 4.5 Maternal smoking, Pregnancyf, % 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
  1. aAdjusted according to consumer price index. Average of incomes at ages 3, 5, 7 and 8 years, or at birth. Used as a categorical variable in the analyses: <500,000, > = 500,000–800,000, > = 800,000–1,100,000, > = 1,100,000
  2. bDichotomized according to Statistics Norway [53]
  3. cGestational age of less than 259 days
  4. dBirth weight of less than 2500 g
  5. eConsumed alcohol once a week or more during either of the trimesters
  6. fSmoked sometimes or daily during the last trimester