Bayer-Oglesby, Lucy
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Personal exposure assessment studies may suffer from exposure-relevant selection bias
2000-07-27, Bayer-Oglesby, Lucy, Rotko, Tuulia, Krütli, Pius, Boudet, Céline, Kruize, Hanneke, Jantunen, Matti, Künzli, Nino
We evaluated exposure-relevant selection bias within the framework of a study on personal air pollution exposure, using traffic data as exposure proxy. Based on random samples of 3000 (Basel) and 2532 (Helsinki) persons, 50 and 250 subjects, respectively, were recruited for direct monitoring and 250 (Basel, Helsinki) for indirect monitoring. In Basel, participants of direct monitoring as compared to non-participants were more likely to live at streets with low traffic volume (49% below 1st quartile vs. 27%). Adjusted for sex, age and nationality, an increase of 100 cars per hour was associated with 14% less participation (odds ratio (OR): 0.861; 95% CI: 0.731, 1.007). Although in Helsinki, traffic volume was neither significantly related to participation in direct nor indirect monitoring, the point estimates indicate a tendency to decreased participation with increasing traffic intensity at home. We conclude that selection bias regarding exposure-relevant characteristics is likely to occur when recruiting participants for studies including demanding personal exposure assessment. Correction for factors routinely collected may not fully account for exposure-relevant bias. This is of particular importance when using exposure data for modelling population exposure distributions, whereas in epidemiological studies, a reduced range of exposure must not a priori distort the exposure-response relationship.
Validity of Annoyance Scores for Estimation of Long Term Air Pollution Exposure in Epidemiologic Studies. The Swiss Study on Air Pollution and Lung Diseases in Adults (SAPALDIA)
2000-07-01, Bayer-Oglesby, Lucy, Künzli, Nino, Monn, Christian, Schindler, Christian, Ackermann-Liebrich, Ursula, Leuenberger, Philippe
In air pollution epidemiology, estimates of long term exposure are often based on measurements made at one fixed site monitor per area. This may lead to exposure misclassification. The present paper validates a questionnaire-based indicator of ambient air pollution levels and its applicability to assess their within-area variability. Within the framework of the SAPALDIA (Swiss Study on Air Pollution and Lung Diseases in Adults) cross-sectional study (1991), 9,651 participants reported their level of annoyance caused by air pollution on an 11-point scale. This subjective measure was compared with annual mean concentrations of particulate matter less than 10 μm in diameter (PM10) and nitrogen dioxide. The impact of individual factors on reported scores was evaluated. Nitrogen dioxide concentrations at home outdoors (measured in 1993), smoking, workplace dust exposure, and respiratory symptoms were found to be predictors of individual annoyance scores. Regression of population mean annoyance scores against annual mean PM10 and nitrogen dioxide concentrations (measured in 1993 and 1991, respectively) across areas showed a linear relation and strong correlations (r > 0.85). Analysis within areas yielded consistent results. The observed associations between subjective and objective air pollution exposure estimates suggest that population mean scores, but not individual scores, may serve as a simple tool for grading air quality within areas. Reported annoyance due to air pollution should be considered an indicator for a complex environmental condition and thus might be used for evaluating the implementation of environmental policies.
Spatial variability of different fractions of particulate matter within an urban environment and between urban and rural sites
2000, Röösli, Martin, Braun-Fährlander, Charlotte, Künzli, Nino, Bayer-Oglesby, Lucy, Theis, Gaston, Camenzind, Markus, Mathys, Patrick, Staehelin, Johannes
The spatial variability of different fractions of particulate matter (PM) was investigated in the city of Basel, Switzerland, based on measurements performed throughout 1997 with a mobile monitoring station at six sites and permanently recorded measurements from a fixed site. Additionally, PM10 measurements from the following year, which were concurrently recorded at two urban and two rural sites, were compared. Generally, the spatial variability of PM4, PM10, and total suspended particulates (TSP) within this Swiss urban environment (area = 36 km2) was rather limited. With the exception of one site in a street canyon next to a traffic light, traffic density had only a weak tendency to increase the levels of PM. Mean PM10 concentration at six sites with different traffic densities was in the range of less than ±10% of the mean urban PM10 level. However, comparing the mean PM levels on workdays to that on weekends indicated that the impact of human activities, including traffic, on ambient PM levels may be considerable. Differences in the daily PM10 concentrations between urban and more elevated rural sites were strongly influenced by the stability of the atmosphere. In summer, when no persistent surface inversions exist, differences between urban and rural sites were rather small. It can therefore be concluded that spatial variability of annual mean PM concentration between urban and rural sites in the Basel area may more likely be caused by varying altitude than by distance to the city center.