title: Occupational exposure to motor exhaust in Stockholm, Sweden--different grouping strategies using variability in NO₂ to create homogenous groups.
abstract: OBJECTIVE
  The aim of the present study was to investigate the personal variability in occupational exposure to NO(2), as a marker of exposure to diesel exhaust, and to compare a statistical method of grouping workers in homogenous groups with a grouping performed by a qualified occupational hygienist.
  
  
  METHODS
  Forty-seven workers exposed to motor exhaust in their occupation were included. Personal measurements of NO(2) were performed with diffusive samplers over three full working shifts. The results from the measurements were analysed with a linear mixed effects model, taking both between and within-worker variability into consideration. The workers were divided into occupational groups in different ways in order to find a categorization, with maximal homogeneity in exposure in each group. We used (B)R(0.95) as an estimator of the between-worker variability. To study the effect of the divisions on the fit of the statistical model, we used the Akaike Information Criterion.
  
  
  RESULTS
  The geometric mean for NO(2) for all 47 workers was 69 μg/m(3) and the between-worker variability (B)R(0.95) was 23.8. In six successive steps, the 47 workers were divided into up to eight groups, based on observed job characteristics. In the final grouping, seven groups were included with geometric means ranging from 32 μg/m(3) for outdoor workers, to 316 μg/m(3) for the most exposed group (tunnel construction workers). The (B)R(0.95) varied between 2.4 and 6.3. The within-worker variability (W)R(0.95) for the last division differed in the groups from 2.0 to 7.9. The Akaike Information Criterion decreased from 246, if all persons were included in one group, to 174 for the final grouping.
  
  
  CONCLUSIONS
  The average level of NO(2) varied about 10 times between the different occupational groups, with the highest level for tunnel construction workers (316 μg/m(3)) and lowest for outdoor workers (32 μg/m(3)). For four of the seven groups the between-worker variability was higher than the within-worker variability.
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden. marie.lewne@ki.se
authors.forename: Marie
authors.initials: M
authors.lastname: Lewné
authors.forename: Nils
authors.initials: N
authors.lastname: Plato
authors.forename: Tom
authors.initials: T
authors.lastname: Bellander
authors.forename: Magnus
authors.initials: M
authors.lastname: Alderling
authors.forename: Per
authors.initials: P
authors.lastname: Gustavsson
mesh_terms: D000395:Air Pollutants, Occupational / Q000032:analysis*; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D009585:Nitrogen Dioxide / Q000032:analysis*; D016273:Occupational Exposure / Q000706:statistics & numerical data*; D013548:Sweden; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000395:Air Pollutants, Occupational; D001335:Vehicle Emissions; D009585:Nitrogen Dioxide