Comparison of Grouping Schemes for Exposure to Total Dust in Cement Factories in Korea.
OBJECTIVE
The purpose of this study was to evaluate grouping schemes for exposure to total dust in cement industry workers using non-repeated measurement data.


METHODS
In total, 2370 total dust measurements taken from nine Portland cement factories in 1995-2009 were analyzed. Various grouping schemes were generated based on work process, job, factory, or average exposure. To characterize variance components of each grouping scheme, we developed mixed-effects models with a B-spline time trend incorporated as fixed effects and a grouping variable incorporated as a random effect. Using the estimated variance components, elasticity was calculated. To compare the prediction performances of different grouping schemes, 10-fold cross-validation tests were conducted, and root mean squared errors and pooled correlation coefficients were calculated for each grouping scheme.


RESULTS
The five exposure groups created a posteriori by ranking job and factory combinations according to average dust exposure showed the best prediction performance and highest elasticity among various grouping schemes.


CONCLUSIONS
Our findings suggest a grouping method based on ranking of job, and factory combinations would be the optimal choice in this population. Our grouping method may aid exposure assessment efforts in similar occupational settings, minimizing the misclassification of exposures.
1. Occupational Safety and Health Research Institute, Korea Occupational Safety and Health Agency, 400, Jongga-ro, Jung-gu, Ulsan 681-230, Korea 3.Present address: Department of Occupational and Environmental Medicine, International St. Mary's Hospital, Catholic Kwandong University, 25, Simgok-ro 100 beon-gil, Seo-gu, Incheon 404-834, Korea koh.donghee@gmail.com.
Dong-Hee
DH
Koh
1. Occupational Safety and Health Research Institute, Korea Occupational Safety and Health Agency, 400, Jongga-ro, Jung-gu, Ulsan 681-230, Korea.
Tae-Woo
TW
Kim
1. Occupational Safety and Health Research Institute, Korea Occupational Safety and Health Agency, 400, Jongga-ro, Jung-gu, Ulsan 681-230, Korea.
Seung Hee
SH
Jang
1. Occupational Safety and Health Research Institute, Korea Occupational Safety and Health Agency, 400, Jongga-ro, Jung-gu, Ulsan 681-230, Korea.
Hyang-Woo
HW
Ryu
2. Department of Environmental Health, National Open University, 86, Daehak-ro, Jong-gu, Seoul 110-791, Korea.
Donguk
D
Park
D000395:Air Pollutants, Occupational / Q000032:analysis; D000465:Algorithms; D060389:Construction Industry; D004391:Dust / Q000032:analysis*; D004784:Environmental Monitoring / Q000295:instrumentation; D006801:Humans; D019570:Inhalation Exposure / Q000032:analysis; D016273:Occupational Exposure / Q000032:analysis* / Q000145:classification; D009790:Occupations; D056910:Republic of Korea
D000395:Air Pollutants, Occupational; D004391:Dust
cement; dust; exposure assessment; grouping; limestone; mixed-effects model