mixture function

Fitting binary mixture models

'mixture' fits a concentration addition, Hewlett or Voelund model to data from binary mixture toxicity experiments.

mixture(object, model = c("CA", "Hewlett", "Voelund"), start, startm, control = drmc())

Arguments

• object: object of class 'drc' corresponding to the model with freely varying EC50 values.
• model: character string. It can be "CA", "Hewlett" or "Voelund".
• start: optional numeric vector supplying starting values for all parameters in the mixture model.
• startm: optional numeric vector supplying the lambda parameter in the Hewlett model or the eta parameters (two parameters) in the Voelund model.
• control: list of arguments controlling constrained optimisation (zero as boundary), maximum number of iteration in the optimisation, relative tolerance in the optimisation, warnings issued during the optimisation.

Details

The function is a wrapper to drm, implementing the models described in Soerensen et al. (2007). See the paper for a discussion of the merits of the different models.

Currently only the log-logistic models are available. Application of Box-Cox transformation is not yet available.

Returns

An object of class 'drc' with a few additional components.

References

Ritz, C. and Streibig, J. C. (2014) From additivity to synergism - A modelling perspective Synergy, 1 , 22--29.

Author(s)

Christian Ritz

See Also

The examples in acidiq (the Hewlett model), glymet (dose/concentration addition) and mecter (the Voelund model).