Analysis of lognormally distributed exposure data with repeated measures and values below the limit of detection using SAS

Details

• Personal Author:
  Deddens JA ; Hein, Misty J. ; Hines CJ ; Jin Y
• Description:
  Studies of determinants of occupational exposure frequently involve left-censored lognormally distributed data, often with repeated measures. Left censoring occurs when observations are below the analytical limit of detection (LOD); repeated measures data results from taking multiple measurements on the same worker. A common method of dealing with this type of data has been to substitute a value (such as LOD/2) for the censored data followed by statistical analysis using the 'usual' methods. Recently, maximum likelihood estimation (MLE) methods have been employed to reduce bias associated with the substitution method. We compared substitution and MLE methods using simulated lognormally distributed exposure data subjected to varying amounts of censoring using two procedures available in SAS: LIFEREG and NLMIXED. In these simulations, the MLE method resulted in less bias and performed well even for censoring up to 80%, whereas the substitution method resulted in considerable bias. We illustrate the NLMIXED procedure using a dataset of chlorpyrifos air measurements collected from termiticide applicators on consecutive days over a 5-day work week. We provide sample SAS code for several situations including one and two groups, with and without repeated measures, random slopes, and nested random effects. [Description provided by NIOSH]
• Subjects:
  Environmental Monitoring Occupational Exposure Occupational Health Safety
• Keywords:
  Air-quality-measurement Air-samples Analytical-instruments Analytical-models Analytical-processes Author Keywords: Censoring Data-processing Exposure-assessment Exposure Determinants Information-retrieval-systems Limit Of Detection LOD Mathematical-models NLMIXED Occupational-exposure Occupational Exposure Repeated Measures SAS Statistical-analysis

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• ISSN:
  0003-4878
• Document Type:
  Text
• Genre:
  Journal Article
• Place as Subject:
  Ohio ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  DSHEFS - Division of Surveillance, Hazard Evaluations, and Field Studies
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  97-112
• Volume:
  55
• Issue:
  1
• NIOSHTIC Number:
  nn:20038224
• Citation:
  Ann Occup Hyg 2011 Jan; 55(1):97-112
• Contact Point Address:
  Yan Jin, Division of Surveillance, Hazard Evaluations and Field Studies, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, Cincinnati, OH 45226, USA
• Email:
  hkn9@cdc.gov
• CAS Registry Number:
  Chlorpyrifos (CAS RN 2921-88-2)
• Federal Fiscal Year:
  2011
• NORA Priority Area:
  Mining ; Manufacturing
• Peer Reviewed:
  True
• Source Full Name:
  Annals of Occupational Hygiene
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:cde7bec564f298e3bd276e44768fea97d530da5f07c43d9b3b285a74f08c3f8c15876d8e204a1bbb72cf93efb143b9ecf2f9b88fc13b361d11ffb3330c6af995
• Download URL:
  https://stacks.cdc.gov/view/cdc/191998/cdc_191998_DS1.pdf
• File Type:
  [PDF - 704.21 KB ]