reverse_helmert_code {contrastable} | R Documentation |
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)
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)
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 ~ reverse_helmert_code)
lm(resp ~ grp, data = mydf)
[Package contrastable version 1.0.2 Index]