“…Personal exposure measurements are often considered as gold standard, since individual activities and exposures in different microenvironments (home, workplace, outdoors, traffic ) are taken into account ( Wallace and Ott, 1982;Wallace et al, 1989;Williams, 1992;Wallace, 1993;Ott and Roberts, 1998 ). However, assessing personal exposures is demanding for participants and, subsequently, such studies are prone to selective non-response and modified time ± activity patterns during measurements (``Hawthorne effect'') (Robinson, 1988;Boudet et al, 1997;Carabin et al, 1999;Grufferman, 1999 ). Such bias is of particular relevance in two fields of application: on the one hand, exposure assessment is a key element of risk assessment (Samet et al, 1998 ).…”