forward_difference_code: Forward difference code

In contrastable: Consistent Contrast Coding for Factors

Forward difference code

Description

Compares the mean of level k to level k+1. Differs in direction from backward_difference_code, so be careful to pick the right function. See also contr.sdif.

Usage

forward_difference_code(n)

Arguments

n	Integer umber of factor levels to compute contrasts for.

Details

Example interpretation for a 4 level factor:

• Intercept = Grand mean (mean of the means of each level)

• grp1 = mean(grp1) - mean(grp2)

• grp2 = mean(grp2) - mean(grp3)

• grp3 = mean(grp3) - mean(grp4)

Value

A contrast matrix with dimensions n rows and (n-1) columns.

Examples

mydf <- data.frame(
  grp = gl(4,5),
  resp = c(seq(1, 5), seq(5, 9), seq(10, 14), seq(15, 19))
)

mydf <- set_contrasts(mydf, grp ~ forward_difference_code)

lm(resp ~ grp, data = mydf)

contrastable documentation built on Oct. 1, 2024, 5:07 p.m.