Materials and methods
Subject recruitment
From dwellings built between 1998 and 2003, 150 households in each year (900 in total) were randomly sampled for questionnaire studies on indoor environmental quality.
In the end, 365 (40.6%) took part in the investigation in 2003; and 91 of them agreed to participate in this study.
It was conducted with all participants’ informed consent and the approval of the
Institutional Ethical Board for Epidemiological Studies at Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences.