## Contrast Matrices

## Usage

    contr.helmert(n, contrasts=TRUE)
    contr.poly(n, contrasts=TRUE)
    contr.sum(n, contrasts=TRUE)
    contr.treatment(n, contrasts=TRUE)

## Value

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

These functions are used for creating contrast matrices for use in fitting analysis of variance and regression models. The columns of the resulting matrices 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 an additional column of ones is prepended to the matrix.

## See Also

`contrasts`, `glm`, `lm`.

[Package Contents]