R: Check Whether One or More Parameter Combinations in a gnm...

checkEstimable {gnm} | R Documentation

## Check Whether One or More Parameter Combinations in a gnm Model are Identified

### Description

For each of a specified set of linear combinations of parameters from a `gnm` model, checks numerically whether the combination's estimate is invariant to re-parameterization of the model.

### Usage

    checkEstimable(model, combMatrix = diag(length(coef(model))),
                   tolerance = NULL)

### Arguments

`model` | a model object of class `"gnm"`
`combMatrix` | numeric: either a vector of length the same as `length(coef(model))`, or a matrix with that number of rows. Coefficients of one or more linear combinations of the model's parameters.
`tolerance` | numeric: a threshold value for detection of non-estimability. If `NULL`, the default value of the `tol` argument to `rankMatrix` is used.

### Value

A logical vector of length equal to the number of parameter combinations tested; `NA` where a parameter combination is identically zero.

### Author(s)

David Firth and Heather Turner

### References

Catchpole, E.A. and Morgan, B.J.T. (1997). Detecting parameter redundancy. Biometrika, 84, 187–196.

### See Also

`gnm`, `se`, `getContrasts`

### Examples

    set.seed(1)

    ## Fit the "UNIDIFF" mobility model across education levels
    unidiff <- gnm(Freq ~ educ*orig + educ*dest +
                   Mult(Exp(educ), orig:dest), family = poisson,
                   data = yaish, subset = (dest != 7))

    ## Check whether multiplier contrast educ4 - educ5 is estimable
    ofInterest(unidiff) <- pickCoef(unidiff, "[.]educ")
    mycontrast <- numeric(length(coef(unidiff)))
    mycontrast[ofInterest(unidiff)[4:5]] <- c(1, -1)
    checkEstimable(unidiff, mycontrast)
    ## should be TRUE

    ## Check whether multiplier educ4 itself is estimable
    mycontrast[ofInterest(unidiff)[5]] <- 0
    checkEstimable(unidiff, mycontrast)
    ## should be FALSE -- only *differences* are identified here

[Package gnm version 1.0-8 Index]