Handling of dioxin measurement data in the presence of non-detectable values: Overview of available methods and their application in the Seveso chloracne study

Andrea Baccarelli, Ruth Pfeiffer, Dario Consonni, Angela C. Pesatori, Matteo Bonzini, Donald G. Patterson, Pier Alberto Bertazzi, Maria Teresa Landi

Research output: Contribution to journalArticle


Exposure measurements of concentrations that are non-detectable or near the detection limit (DL) are common in environmental research. Proper statistical treatment of non-detects is critical to avoid bias and unnecessary loss of information. In the present work, we present an overview of possible statistical strategies for handling non-detectable values, including deletion, simple substitution, distributional methods, and distribution-based imputation. Simple substitution methods (e.g., substituting 0, DL/2, DL/√2, or DL for the non-detects) are the most commonly applied, even though the EPA Guidance for Data Quality Assessment discouraged their use when the percentage of non-detects is >15%. Distribution-based multiple imputation methods, also known as robust or "fill-in" procedures, may produce dependable results even when 50-70% of the observations are non-detects and can be performed using commonly available statistical software. Any statistical analysis can be conducted on the imputed datasets. Results properly reflect the presence of non-detectable values and produce valid statistical inference. We describe the use of distribution-based multiple imputation in a recent investigation conducted on subjects from the Seveso population exposed to 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD), in which 55.6% of plasma TCDD measurements were non-detects. We suggest that distribution-based multiple imputation be the preferred method to analyze environmental data when substantial proportions of observations are non-detects.

Original languageEnglish
Pages (from-to)898-906
Number of pages9
Issue number7
Publication statusPublished - Aug 2005



  • 2,3,7,8-Tetrachlorodibenzo-p-dioxin
  • Detection limit
  • Exposure assessment
  • Multiple imputation
  • Non-detects
  • Seveso

ASJC Scopus subject areas

  • Environmental Chemistry
  • Environmental Science(all)

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