# contr.sdif

From MASS v7.3-0
by Brian Ripley

##### Successive Differences contrast coding

A coding for unordered factors based on successive differences.

- Keywords
- models

##### Usage

`contr.sdif(n, contrasts = TRUE)`

##### Arguments

- n
- The number of levels required.
- contrasts
- Should there be
`n - 1`

columns orthogonal to the mean (the default) or`n`

columns spanning the space.

##### Details

The contrast coefficients are chosen so that the coded coefficients in a one-way layout are the differences between the means of the second and first levels, the third and second levels, and so on.

##### Value

- If
`contrasts is`

`TRUE`

, a matrix with`n`

rows and`n - 1`

columns, and the`n`

by`n`

identity matrix if`contrasts`

is`FALSE`

.

##### References

Venables, W. N. and Ripley, B. D. (2002)
*Modern Applied Statistics with S.*
Fourth Edition, Springer.

##### See Also

##### Examples

`contr.sdif(6)`

*Documentation reproduced from package MASS, version 7.3-0, License: GPL-2 | GPL-3*

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