## Abstract

Pharmacokinetic studies of biomarkers for environmental contaminants in humans are generally restricted to a few measurements per subject taken after the initial exposure. Subjects are selected for inclusion in the study if their measured body burden is above a threshold determined by the distribution of the biomarker in a control population. Such selection procedures introduce bias in the ordinary weighted least squares estimate of the decay rate λ caused by the truncation. We show that if the data are conditioned to lie above a line with slope - λ on the log scale then the weighted least squares estimate of λ is unbiased. We given an iterative estimation algorithm that produces this unbiased estimate with commercially available software for fitting a repeated measures linear model. The estimate and its efficacy are discussed in the context of a pharmacokinetic study of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Unbiasedness and efficiency are demonstrated with a simulation.

Original language | English (US) |
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Pages (from-to) | 165-174 |

Number of pages | 10 |

Journal | Environmetrics |

Volume | 9 |

Issue number | 2 |

State | Published - Mar 1 1998 |

Externally published | Yes |

## Keywords

- Biomarker
- Decay rate
- Least squares
- Regression toward the mean

## ASJC Scopus subject areas

- Statistics and Probability
- Ecological Modeling