Stavex: A Sophisticated but User-Friendly Expert System for the Design and Analysis of Experiments
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Drug Information Journal, Vol. 31, pp. 597-606, 1997 Printed in the USA. All rights reserved.
STAVEX: A SOPHISTICATED BUT USER-FRIENDLY EXPERT SYSTEM FOR THE DESIGN AND ANALYSIS OF EXPERIMENTS YVES-LAURENT GRIZE
WOLFGANG SEEWALD AND
Mathematical Applications in Chemistry and Physics, Ciba-Geigy Ltd., Basel, Switzerland
STAVEX enables experimenters in research and development to apply statistical design and analysis of experiments in their routine work independently of a statistician. STAVEX presents expert knowledge in industrial statistics in the language of practitioners. The system can handle process factors, such as temperature or concentration, as well as mixture factors which have to satisfy a summing-up condition, for example, typical in galenic formulations. The STAVEX philosophy is based on the three typical stages of statistical experimental design: screening, modeling, and optimization. During the first two stages the goal is factor reduction. It is recommended to begin experimentation with a large (say more than eight) number of factors. In the final optimization stage, the number of factors is small (three or less); then, a quadratic model is fitted which should allow for good predictions. STAVEX guides the users through these different experimentation stages, writes reports, suggests a look at appropriate graphical displays (such as half-normal plots or overlaid contour plots) to help in the interpretation and understanding of the results, and provides extensive model diagnostics concerning outlier detection, transformations, and model deviations, STAVEX runs on PCs under Microsoft Windows 3.1, Windows NT or Windows 95. Key Words: Statistical experimental design; Statistical analysis of experiments; Expert system; PC program; Mixtures
INTRODUCTION
Research and product development, Process development, and 0 Process optimization and validation. 0
STAVEX is PC-based (Windows) easy-touse software to assist the chemist or engineer in the design and analysis of industrial experiments. Its main applications are in:
Presented at the DIA Workshop “Statistical Methodology in Non-Clinical and Toxicological Studies,” March 25-27, 1996, Bruaes, - Belgium. Reprint address: Dr. Yves-Laurent Grize, CibaGeigy Ltd., CH-4002 Basel, Switzerland.
STAVEX was developed within Ciba and speaks the language of the chemisdengineer. It obliges the user to structure problems and to solve them strategically, and includes special features such as: Combination of process and mixture factors, 0 Multiresponse problem formulations,
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5Y8
TABLE 1 Design Stages in STAVEX
Stage
Screening
>8 Number of factors Model linear Design (super-) saturated Analysis half-normal plot
Aim
Modeling
Optimization
4-8
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