Optimal designs for estimating critical effective dose under model uncertainty in a dose response study

Toxicologists have been increasingly using a class of models to describe a continuous response in the last few years. This class consists of nested nonlinear models and is used for estimating various parameters in the models or some meaningful function of the model parameters. Our work here is first to address design issues for this popular class of models among toxicologists. Specifically we construct a variety of optimal designs under model uncertainty and study their properties for estimating the critical effective dose (CED), which is model dependent. Two types of optimal designs are proposed: one type maximizes the minimum of efficiencies for estimating the CED regardless which member in the class of models is the appropriate model, and (ii) maximin compound optimal design that simultaneously selects the most appropriate model and provides the best estimate for CED at the same time. We compare relative efficiencies of these optimal designs and commonly used designs for estimating CED. To facilitate use of these designs, we have constructed a website that practitioners can generate tailor-made designs for their settings

Recruitment Dynamics of the Gulf of Riga Herring Stock: Density-Dependent and Environmental Effects

The Gulf of Riga and open-sea stocks of the Baltic herring have displayed remarkably consistent inverse recruitment and stock development patterns since the 1970s: the open-sea stocks steadily declined, whereas the Gulf stock increased rapidly in the early 1990s, reaching a peak abundance in the early 2000s and exceeding the level of the 1970s by a factor of 2¿3. The increase was accompanied by a decline in the mean weight-at-age and the condition factor. The estimated decline (by 30¿40%) in the average annual consumption rate per individual and changes observed in the zooplankton community suggest that density-dependent effects may have increased since the 1970s. The current period of high stock sizes is also characterized by greater recruitment variability. Historical fecundity investigations have established that the average egg production per individual has decreased in all age groups by 20¿ 50%, along with a decrease in mean weight and condition. Yet, the effect on recruitment has been low so far, because lower fecundity has been compensated by the greater abundance and population fecundity has been maintained at the original level. Recruitment appears to be more influenced by environmental conditions than by spawning-stock biomass.JRC.G.4-Maritime affair

Optimal designs for estimating the coefficients of the lower frequencies in trigonometric regression models

Trigonometric regression model, c-Optimal design, Chebyshev approximation, Two dimensional shape analysis,