R: Contrast matrices

contr.cum {Epi} | R Documentation

## Contrast matrices

### Description

Return a matrix of contrasts for factor coding.

### Usage

      contr.cum(n)
      contr.diff(n)
      contr.2nd(n)
      contr.orth(n)

### Arguments

`n` | A vector of levels for a factor, or the number of levels.

### Details

These functions are used for creating contrast matrices for use in fitting regression models. The columns of the resulting matrices contain contrasts which can be used for coding a factor with `n` levels.

`contr.cum` gives a coding corresponding to successive differences between factor levels.

`contr.diff` gives a coding that correspond to the cumulative sum of the value for each level. This is not meaningful in a model where the intercept is included, therefore `n` columns ia always returned.

`contr.2nd` gives contrasts corresponding to 2nd order differences between factor levels. Returns a matrix with `n-2` columns.

`contr.orth` gives a matrix with `n-2` columns, which are mutually orthogonal and orthogonal to the matrix `cbind(1,1:n)`

### Value

A matrix with `n` rows and `k` columns, with `k`=`n` for `contr.diff` `k`=`n-1` for `contr.cum` `k`=`n-2` for `contr.2nd` and `contr.orth`.

### Author(s)

Bendix Carstensen

### See Also

`contr.treatment`

### Examples

    contr.cum(6)
    contr.2nd(6)
    contr.diff(6)
    contr.orth(6)

[Package Epi version 2.42 Index]