contr.SAS {nlme} | R Documentation

## Contrast Matrices

### Description

Return a matrix of contrasts corresponding to the parameterization for a factor used in SAS.

### Usage

    contr.SAS(n, contrasts=TRUE)

### Arguments

`n` | a vector of levels for a factor, or the number of levels.
`contrasts` | a logical indicating whether contrasts should be computed.

### Details

This function is used for creating contrast matrices for use in fitting analysis of variance and regression models. The columns of the resulting matrix contain contrasts which can be used for coding a factor with `n` levels. The returned value contains the computed contrasts. If the argument `contrasts` is `FALSE` then a square indicator matrix is returned.

These contrasts are similar to those from `contr.treatment` except that they represent shifts relative to the last level of the factor, not the first level. This generates the same parameterization for a linear model as is used in SAS (see http://www.sas.com).

### Value

A matrix with `n` rows and `k` columns, with `k=n-1` if `contrasts` is `TRUE` and `k=n` if `contrasts` is `FALSE`.

### Author(s)

Jose Pinheiro jcp@research.bell-labs.com, Douglas Bates bates@stat.wisc.edu

### See Also

`contr.treatment`

### Examples

    contr.SAS(4)

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