mixture {drc} | R Documentation |
'mixture' fits a concentration addition, Hewlett or Voelund model to data from mixture toxicity experiments.
mixture(formula, curve, collapse, weights, data = NULL, boxcox = FALSE, bcAdd = 0, varPower = FALSE, startVal, fct = l4(), na.action = na.fail, robust = "mean", type = "continuous", cm = NULL, logDose = NULL, control = mdControl(), model = "Hewlett", startVal2)
formula |
a symbolic description of the model to be fit. Either of the form 'response ~ dose' or as a data frame with response value in first column and dose in second column. |
curve |
a numeric vector (percentages!) containing the grouping of the data. |
collapse |
a formula starting with a tilde, specifying the model for the b parameter in the logistic model (the only 'free' parameter). |
weights |
a numeric vector containing weights. |
data |
a data frame containing the variables in the model. This argument is not optional! |
boxcox |
logical or numeric. If TRUE the optimal Box-Cox transformation is applied to the model. If FALSE (the default) no Box-Cox transformation is applied. If numeric the specified value is used in the Box-Cox transformation. |
bcAdd |
a numeric value specifying the constant to be added on both sides prior to Box-Cox transformation. The default is 0. |
varPower |
logical. If TRUE the variance is modelled as a power function of the mean. If FALSE (the default) no variance modelling is applied. |
startVal |
an optional numeric vector containing start values for all parameters in the model. Overrules any self starter function. |
fct |
a list with three or 5 elements specifying the non-linear function, the accompanying self starter function, the names of the parameter in the non-linear function and, optionally, the first and second derivatives. |
na.action |
a function which indicates what should happen when the data contain 'NA's. The default is 'na.fail'. To omit 'NA's use 'na.omit'. |
robust |
a character string specifying the rho function for robust estimation. Default is non-robust least squares estimation ("mean"). Available robust methods are: median estimation ("median"), least median of squares ("lms"), least trimmed squares ("lts"), metric trimming ("trimmed"), metric winsorizing ("winsor") and Tukey's biweight ("tukey"). |
type |
a character string specifying the data type: binomial and continuous are the only options currently. |
cm |
character string or numeric value specifying the level in curve corresponding to control measurements. |
logDose |
a numeric value or NULL. If log doses value are provided the base of the logarithm should be specified (exp(1) for the natural logarithm and 10 for 10-logarithm). |
control |
a 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. |
model |
a character string. It can be "CA", "Hewlett" or "Voelund". |
startVal2 |
an optional numeric vector supplying the lambda parameter in the Hewlett model or the eta parameters (two parameters) in the Voelund model. |
The function is a wrapper to multdrc
, implementing the models described in S{o}rensen et al. (2006). See the paper for a
discussion of the merits of the different models.
An object of class 'drc'.
Christian Ritz
S{o}rensen, H. and Cedergreen, N. and Skovgaard, I. M. and Streibig, J. C. (2006) An isobole-based statistical model and test for synergism/antagonism in binary mixture toxicity experiments, Statistical Ecology and Environmental Statistics, 13. ?–??.
The function has argument similar to those in multdrc
.
## See the example under ?acidiq