Sample and survey
The study included inhabitants living in Oslo. Data on residential addresses were obtained from the Norwegian Public Roads Administration in connection with their ongoing work on noise mapping. Selection of the study areas was based on traffic density maps and crude data on noise levels recorded at the most exposed façade of the residential buildings. From the home addresses, an age- and gender-stratified sample of 5390 persons in Oslo, the largest city of Norway was selected using the central Norwegian person registry (49% female and 51% male > 18 years). A self-administered questionnaire together with an introductory letter was mailed to the population sample in October 2000. To avoid possible bias in responses to the noise questions, we presented the study as a general investigation into health and quality of life, with no specific focus on noise. A total of 3262 respondents (60.5 %) answered and returned the questionnaire. 145 respondents who had either moved or whose home address was not verifiable were excluded from the analyses. A total of 3117 respondents (51.1% female and 48.9% male) were used for the further analyses. The study was approved by The Regional Committee for Medical Research Ethics in Norway.