Models for the estimation of a ‘no effect concentration’

Abstract

SUMMARYThe 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, pro®le likelihood and asymptotic normality). The adequacy of these methods is empirically con®rmed by the results of a simulation study. The pro®le 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 ef¯uent.

Estimating regression models with unknown break‐points

“…These values are called break-points, change-points, transition-points or switch-points [1,2]; the word 'threshold' is also used [3], but some authors use it just when there is no e ect on the response before of such a value [4,5]. In toxicology the 'no-observede ect-level' or 'no-e ect-concentration' are strictly related to meaning threshold value [6,7]. Non-linear relationships with break-points are said to be piecewise, segmented, broken-line or multi-phase regressions [8][9][10][11].…”

A validated algorithm for selecting non-toxic chemical concentrations_suppl1

“…In general, the sigmoidal dose-response model used in our study for the determination of NtCs fitted the measured data better than the threshold approach that delivered NEC values (Pires et al, 2002). In addition, in 90 out of 91 cases (in one NtC = NEC), NtCs were more protective than NECs.…”

“…NtC values were compared with NEC values calculated in this study by applying the approach proposed by Pires et al (2002). In this threshold model, NEC can be determined by fitting the following equation to the measured data: (Eq.…”

Effect of PFOA/PFOS pre-exposure on the toxicity of the herbicides 2,4-D, Atrazine, Diuron and Paraquat to a model aquatic photosynthetic microorganism

“…No effect concentration has been proposed as an alternative to NOECs. The NEC model is a dose-response model with a threshold parameter (the NEC) below which the response is assumed to be constant and equal to the control response (Pires et al, 2002).…”