R: Conversion between a model object and a restriction matrix

model-coerce {pbkrtest} | R Documentation

## Conversion between a model object and a restriction matrix

### Description

Testing a small model under a large model corresponds imposing restrictions on the model matrix of the larger model and these restrictions come in the form of a restriction matrix. These functions converts a model to a restriction matrix and vice versa.

### Usage

    model2restrictionMatrix(largeModel, smallModel)

    ## S3 method for class 'merMod'
    model2restrictionMatrix(largeModel, smallModel)

    ## S3 method for class 'lm'
    model2restrictionMatrix(largeModel, smallModel)

    restrictionMatrix2model(largeModel, LL)

    ## S3 method for class 'merMod'
    restrictionMatrix2model(largeModel, LL)

    ## S3 method for class 'lm'
    restrictionMatrix2model(largeModel, LL)

### Arguments

`largeModel, smallModel` | Model objects of the same "type". Possible types are linear mixed effects models and linear models (including generalized linear models)
`LL` | A restriction matrix.

### Value

`model2restrictionMatrix`: A restriction matrix. `restrictionMatrix2model`: A model object.

### Note

That these functions are visible is a recent addition; minor changes may occur.

### Author(s)

Ulrich Halekoh uhalekoh@health.sdu.dk, Søren Højsgaard sorenh@math.aau.dk

### References

Ulrich Halekoh, Søren Højsgaard (2014)., A Kenward-Roger Approximation and Parametric Bootstrap Methods for Tests in Linear Mixed Models - The R Package pbkrtest., Journal of Statistical Software, 58(10), 1-30., http://www.jstatsoft.org/v59/i09/

### See Also

`PBmodcomp`, `PBrefdist`, `KRmodcomp`

### Examples

    library(pbkrtest)
    data("beets", package = "pbkrtest")
    sug <- lm(sugpct ~ block + sow + harvest, data=beets)
    sug.h <- update(sug, .~. - harvest)
    sug.s <- update(sug, .~. - sow)

    ## Construct restriction matrices from models
    L.h <- model2restrictionMatrix(sug, sug.h); L.h
    L.s <- model2restrictionMatrix(sug, sug.s); L.s

    ## Construct submodels from restriction matrices
    mod.h <- restrictionMatrix2model(sug, L.h); mod.h
    mod.s <- restrictionMatrix2model(sug, L.s); mod.s

    ## The models have the same fitted values
    plot(fitted(mod.h), fitted(sug.h))
    plot(fitted(mod.s), fitted(sug.s))
    ## and the same log likelihood
    logLik(mod.h)
    logLik(sug.h)
    logLik(mod.s)
    logLik(sug.s)

[Package pbkrtest version 0.4-7 Index]