title: Sampling strategies for occupational exposure assessment under generalized linear model.
abstract: OBJECTIVE
  Occupational exposure assessment is a major task in industrial hygiene studies. Although statistical analyses for magnitudes and variations of exposures to various types of working populations based on existing data sets are extensive, relatively few discussions on study designs appear in the literature, especially for sample size determination and number of repeated measurements.
  
  
  METHODS
  In this paper, we propose a general framework of sampling strategies on sample size requirement together with the number of repeated measurements using the mixed-effects generalized linear model (GLM). As illustrative examples, we discuss sampling strategies separately under the log-normal assumption for hypotheses testing on (i) mean exposure differences of multiple worker groups and (ii) presence of a long-term exposure trend.
  
  
  RESULTS
  Given a specified alternative hypothesis, the desired significance level and statistical power, the number of repeated measurements, within-worker and between-worker variances, and a correlation structure, we have derived and tabulated an explicit sample size requirement of the two hypothetical cases under log-normal distribution assumption.
  
  
  CONCLUSIONS
  On the basis of the tabulated outcomes, the sample size requirement is much more dominant than the number of repeated measurements for a group exposure comparison. Thus, in this case, recruiting more workers with fewer repeated measurements may be more economical than the opposite approach. For testing the presence of a long-term exposure trend, the sample size required decreases substantially with the number of repeated measurements. Also, equally spaced sampling times would be optimal because the effect of between-worker variance is algebraically cancelled out in sample size calculations.
authors.affiliation: Division of Biostatistics and Bioinformatics, Institute of Population Health Sciences, National Health Research Institutes, Zhunan Town, Miaoli County 350, Taiwan. ccchen@nhri.org.tw
authors.forename: Chu-Chih
authors.initials: CC
authors.lastname: Chen
authors.forename: Cheng-Lin
authors.initials: CL
authors.lastname: Chuang
authors.forename: Kuen-Yuh
authors.initials: KY
authors.lastname: Wu
authors.forename: Chang-Chuan
authors.initials: CC
authors.lastname: Chan
mesh_terms: D004784:Environmental Monitoring / Q000379:methods; D015386:Hazardous Substances / Q000032:analysis*; D006801:Humans; D019570:Inhalation Exposure / Q000032:analysis; D016014:Linear Models; D016273:Occupational Exposure / Q000032:analysis*; D016272:Occupational Health / Q000706:statistics & numerical data*; D018401:Sample Size
chemical_list: D015386:Hazardous Substances