Models for the estimation of a ‘no effect concentration’

Authors

  • Ana M. Pires,

    Corresponding author
    1. Department of Mathematics and Applied Mathematics Centre, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
    • Department of Mathematics, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
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  • João A. Branco,

    1. Department of Mathematics and Applied Mathematics Centre, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
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  • Ana Picado,

    1. Environmental Technologies Institute, INETI, Az. Lameiros, 1699 Lisboa Codex, Portugal
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  • Elsa Mendonça

    1. Environmental Technologies Institute, INETI, Az. Lameiros, 1699 Lisboa Codex, Portugal
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Abstract

The use of a no effect concentration (NEC), instead of the commonly used no observed effect concentration (NOEC), has been advocated recently. In this article models and methods for the estimation of an NEC are proposed and it is shown that the NEC overcomes many of the objections to the NOEC. The NEC is included as a threshold parameter in a non-linear model. Numerical methods are then used for point estimation and several techniques are proposed for interval estimation (based on bootstrap, profile likelihood and asymptotic normality). The adequacy of these methods is empirically confirmed by the results of a simulation study. The profile likelihood based interval has emerged as the best method. Finally the methodology is illustrated with data obtained from a 21 day Daphnia magna reproduction test with a reference substance, 3,4-dichloroaniline (3,4-DCA), and with a real effluent. Copyright © 2002 John Wiley & Sons, Ltd.

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