| Experimental Designs for Mixtures of Chemicals along Fixed Ratio Rays Stephanie L. Meadows,1 Chris Gennings,2 W.
Hans Carter Jr.,2 and Dong-Soon Bae3 1Pfizer Inc., Groton, Connecticut, USA; 2Department
of Biostatistics, Virginia Commonwealth University, Medical College
of Virginia, Richmond, Virginia, USA; 3Center for Environmental
Toxicology and Technology, Department of Environmental and Radiological
Sciences, Colorado State University, Fort Collins, Colorado, USA Abstract
Experimental design is important when studying mixtures/combinations of chemicals. The traditional approach for studying mixtures/combinations of multiple chemicals involves response surface methodology, often supported by factorial designs. Although such an approach permits the investigation of both the effects of individual chemicals and their interactions, the number of design points needed to study the chemical mixtures becomes prohibitive when the number of compounds increases. Fixed ratio ray designs have been developed to reduce the amount of experimental effort when interest can be restricted to a specific ray. We focus on the design and analysis issues involved in studying mixtures/combinations of compounds along fixed ratio rays of the compounds. To obtain the inference regarding the interactions among the compounds, we show that the only data required are those along the fixed ratio ray. Key words: additivity, interaction index, isobologram. Environ Health Perspect 110(suppl 6) :979-983 (2002) . http://ehpnet1.niehs.nih.gov/docs/2002/suppl-6/979-983meadows/abstract.html
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