The determination of toxicokinetic parameters is an essential component in the risk assessment of potential harmful chemicals. It's a first step to analyse the processes which are involved in the formation of DNA adducts and might therefore lead to the development of cancer. The complete research depends on investigations with animals in vivo and in vitro, so that a critical step is the extrapolation from experimental animals to the human organism. This aim of extrapolation from one species to an other requires a characterisation of  the interesting processes which is valid for the whole species, i.e. population mean parameters instead of different individual parameters which may also vary between repeated examinations of the individuals and between different doses. Nevertheless these differences are of great importance to have a more precise insight into the variability structure of the toxicokinetic processes. The theory of hierarchical models provides a procedure which incorporates both, a  modelling of the variability structure and of population mean processes, furthermore allowing the incorporation of prior information, which is often available in toxicokinetic research. The present approach is part of a strategy to determinate the processes of uptake, elimination, and metabolism of the gas ethylene which is a natural body constituent and an important industrial chemical.

WOLFGANG URFER
Unisertitat Dortmund
Fachbereich Statistik - Lehrstuhl fur Statistik in der Genetik
Vogelpothsweg 87
Dortmund 44221, Germany
urfer@omega.statistik.uni-dortmund.de
 
 

Todays progress of the various erosion types in the world is of such degree that it should concern all of us and not only the effected countries. To control the extension of  erosion in the future, many countries set up long duration observation wards to discover the long term developement of soil loss. The data handled in this study, are long duration erosion observations from morocco of soil leveled down by water. To be precise, we have two climatically different regions, each dived in neighboured plots in the water catchment area of Rabat. The measured data grasp soil loss and different compositions of the plots. Standard statistical methods such as analysis of variance, regression analysis, factor analysis and time series applications, surprisingly supply results of easy interpretation. It is shown that such analysis can be done with standard statistical programs, SAS® for instance, without the use of any special spatial program package. An extension of such an analysis is within the sphere of a geographic information system and will be discussed in the outlook.

MATTHIAS ZERBST
Universitat Dortmund
Inst. fur Wirtschafts- und Sozialstatistik
Vogelpothsweg 78
Dortmund 44221, Germany
su1051@studserver.uni-dortmund.de