R: Comparison of parameters

compParm {drc} | R Documentation

## Comparison of parameters

### Description

Compare parameters from different assays, either by means of ratios or differences.

### Usage

      compParm(object, strVal, operator = "/", vcov. = vcov, od = FALSE,
      pool = TRUE, display = TRUE)

### Arguments

`object` | an object of class 'drc'.
`strVal` | a name of parameter to compare.
`operator` | a character. If equal to "/" (default) parameter ratios are compared. If equal to "-" parameter differences are compared.
`vcov.` | function providing the variance-covariance matrix. `vcov` is the default, but `sandwich` is also an option (for obtaining robust standard errors).
`od` | logical. If TRUE adjustment for over-dispersion is used.
`pool` | logical. If TRUE curves are pooled. Otherwise they are not. This argument only works for models with independently fitted curves as specified in `drm`.
`display` | logical. If TRUE results are displayed. Otherwise they are not (useful in simulations).

### Details

The function compares actual parameter estimates, and therefore the results depend on the parameterisation used. Probably it is most useful in combination with the argument `collapse` in `drm` for specifying parameter constraints in models, either through data frames or lists with formulas without intercept (-1).

### Value

A matrix with columns containing the estimates, estimated standard errors, values of t-statistics and p-values for the null hypothesis that the ratio equals 1 or that the difference equals 0 (depending on the `operator` argument).

### Author(s)

Christian Ritz

### Examples

    # Fitting a model with names assigned to the parameters!
    spinach.m1 <- drm(SLOPE~DOSE, CURVE, data = spinach,
    fct = LL.4(names = c("b", "lower", "upper", "ed50")))

    ## Calculating ratios of parameter estimates for the parameter named "ed50"
    compParm(spinach.m1, "ed50")

    ## Calculating differences between parameter estimates for the parameter named "ed50"
    compParm(spinach.m1, "ed50", "-")

[Package drc version 3.0-1 Index]