The impact of noise intrusion on sleep and daytime functioning is well illustrated in the literature, where results of both laboratory and field studies are reported (Griefahn 2002; Muzet 2007). One challenge in the elaboration of field studies on the impact of road traffic noise on sleep concerns the indoor noise assessment. Only a few field studies assessed indoor noise levels on a daily basis (Eberhardt & Akselsson 1987; Vallet et al. 1983). Other large-scaled field studies - though showing consistent results for sleep disturbances - were unable to collect individual noise levels due to large population samples and therefore needed to rely on outside noise measurements (Ohrstrom 1991 & 1989; Belojevic & Jakovljevic 1997; Stosic et al. 2009). Another element that complicates field studies on noise and sleep is the fact that in addition to noise exposure, a large number of mediating factors play an important role in the contribution of noise to sleep disturbances (Ouis 2001; Muzet 2007). Of the many mediating factors investigated, little research was performed on the effects of the bedroom location on the relation between inside and outside noise levels, on noise perception and on sleep disturbances in highly noise exposed regions. One study performed by Ohrstrom (1993) reported a decrease in sleep quality, longer sleep onset latencies and lower values in terms of psycho-social wellbeing in subjects sleeping at the street side compared to subjects sleeping at the backside of their houses, both located in high density of road traffic regions. In most studies, this issue is addressed by putting the bedroom orientation as an inclusion criterion (e.g. all street side) or by measuring noise levels outside at the bedroom fagade (Ohrstrom 1991; Ohrstrom & Skanberg 2004; Stosic et al. 2009). Other studies derived the bedroom location from questionnaires and corrected the noise levels outside according to it (Ohrstrom 1989, 2004; Belojevic & Jakovljevic 1997).
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