Successive Differences contrast coding

DESCRIPTION:

A coding for unordered factors based on successive differences.

USAGE:

contr.sdif(n, contrasts = T)

REQUIRED ARGUMENTS:

n
The number of levels required.

OPTIONAL ARGUMENTS:

contrasts
Should there be n - 1 columns orthogonal to the mean (the default) or n columns spanning the space.

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.

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.

REFERENCES:

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

SEE ALSO:

, ,

EXAMPLES:

contr.sdif(6)