Table 1.
Characteristics of the study population in total, by three categories of traffic noise exposure (Len).
| Covariate | Total Study Sample (n = 2665) | |||
|---|---|---|---|---|
| <40 dB | 40–50 dB | >50 dB | Total | |
| n (%) | 455 (17.1) | 1321(49.6) | 889 (33.4) | 2665 |
| % male | 54.3 | 50.3 | 47.6 | 50.1 |
| Sleep duration (%) | ||||
| >10 h | 19.0 | 49.0 | 32.0 | 27.5 |
| 10 h | 16.6 | 50.3 | 33.1 | 57.5 |
| <10 h | 15.5 | 47.8 | 36.8 | 15.0 |
| Sleep problems (% yes) | 2.6 | 2.4 | 3.6 | 2.9 |
| Gross annual household income a (NOK), mean (SD) | 1,057,762 (686,380) | 1,070,305 (923,924) | 893,990 (598,621) | 100,9347 (793,343) |
| Season, questionnaire completion (%) | ||||
| Winter | 19.5 | 46.8 | 33.7 | 23.6 |
| Spring | 16.2 | 48.5 | 35.3 | 23.9 |
| Summer | 15.6 | 51.9 | 32.6 | 20.8 |
| Fall | 16.9 | 50.9 | 32.2 | 31.7 |
| Urbanity b (%) | ||||
| Outskirts | 20.2 | 53.3 | 26.5 | 71.8 |
| Semi-central | 11.1 | 48.6 | 40.2 | 20.5 |
| Center | 3.4 | 17.1 | 79.5 | 7.7 |
| Age (months), mean (SD) | 85.5 (1.5) | 85.4 (1.6) | 85.4 (1.6) | 85.4 (1.6) |
| Mother’s education (%) | ||||
| >4 years university/college | 17.2 | 52.1 | 30.7 | 41.6 |
| ≤4 years university/college | 17.8 | 48.4 | 33.7 | 44.2 |
| High school | 14.2 | 45.8 | 40.0 | 14.3 |
| Ethnicity c (%) | ||||
| Non-Western | 15.1 | 39.6 | 45.3 | 10.4 |
| Western | 17.3 | 50.7 | 32.0 | 89.6 |
| Siblings < age 4 (%) | ||||
| Yes | 18.1 | 49.8 | 32.2 | 37.0 |
| No | 16.5 | 49.4 | 34.1 | 63.0 |
| Type of building (%) | ||||
| Detached house | 19.5 | 57.7 | 22.8 | 22.4 |
| Semi-detached | 19.4 | 54.0 | 26.6 | 46.3 |
| Apartment | 12.0 | 37.2 | 50.8 | 31.3 |
| Rail traffic noise (Len) | ||||
| 0 dB | 59.6 | 48.4 | 40.7 | 47.7 |
| ≤30 dB | 20.2 | 24.8 | 17.3 | 21.5 |
| >30 dB | 20.2 | 26.9 | 42.0 | 30.8 |
a Adjusted according to consumer price index. b Outskirts: outside the Ring 3 road. Between: between roads Ring 2 and Ring 3; Center: inside Ring 2 road. The covariate indicated how far the children lived from the city center. c Dichotomized according to Statistics Norway [49]. NOK = Norwegian kroner. SD = standard deviation.