contrastable (version 1.0.2)

reverse_helmert_code: Reverse Helmert code

Description

Reverse helmert coding is the same concept as helmert coding, but the order of the groupings is reversed. See also helmert_code.

Usage

reverse_helmert_code(n)

Value

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

Arguments

n

Integer umber of factor levels to compute contrasts for.

Details

Reverse helmert coding compares each level to the total mean of all levels that come after it. Differs from forward difference coding, which only compares pairs of levels (not a level to a cumulative mean of levels).

Example interpretation for a 4 level factor:

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

• grp1 = mean(grp4, grp3, grp2) - grp(1)

• grp2 = mean(grp4, grp3) - mean(grp2)

• grp3 = mean(grp3) - mean(grp4)

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 ~ reverse_helmert_code)
lm(resp ~ grp, data = mydf)