forward_difference_code {contrastable} | R Documentation |
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)
[Package contrastable version 1.0.2 Index]