Analysis of mixtures of drugs/chemicals along a fixed-ratio ray without single-chemical data to support an additivity model

  • Stephanie L. Meadows-Shropshire
  • Chris Gennings
  • W. Hans Carter
  • Jane Ellen Simmons


This article presents and illustrates an approach to designing and analyzing studies involving mixtures/combinations of drugs or chemicals along fixed-ratio rays of the drugs or chemicals for generalized linear models. When interest can be restricted to a specific ray, we consider fixed-ratio ray designs to reduce the amount of experimental effort. When a ray design is used, we have shown that the hypothesis of additivity can be rejected when higher order polynomial terms are required in the total dose-response model. Thus, it is important that we have precise parameter estimates for these higher order polynomial terms in the linear predictor. We have developed methodology for finding a D s -optimal design based on this subset of the terms in the linear predictor.

Key Words

D-optimality Ds-optimality 


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Copyright information

© International Biometric Society 2004

Authors and Affiliations

  • Stephanie L. Meadows-Shropshire
    • 1
  • Chris Gennings
    • 2
  • W. Hans Carter
    • 2
  • Jane Ellen Simmons
    • 3
  1. 1.Clinical Statistics at Pfizer, IncNew London
  2. 2.Department of BiostatisticsVirginia Commonwealth UniversityRichmond
  3. 3.U.S. EPA-National Health and Environmental Effects LaboratoryResearch Triangle Park

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