contr.FrF2: Contrasts for orthogonal Fractional Factorial 2-level designs
Description
Contrasts for orthogonal Fractional Factorial 2-level designs
Usage
contr.FrF2(n, contrasts=TRUE)
Arguments
n
power of 2; number of levels of the factor for which contrasts are
to be generated
contrasts
must always be TRUE; option needed for
function model.matrix to work properly
Value
The function returns orthogonal contrasts for factors with number of levels a power of 2.
All contrast columns consist of -1 and +1 entries (half of each).
If factors in orthogonal arrays
with 2-level factors are assigned these contrasts, the columns of the model matrix
for the main effects model are orthogonal to each other and to the column for the intercept.
Details
This function mainly supports -1/+1 contrasts for 2-level factors.
It does also work if the number of levels is a power of 2.
For more than four levels, the levels of the factor must be in an appropriate order
in order to guarantee that the columns of the model matrix for an FrF2-derived structure
are orthogonal.
# NOT RUN {## assign contr.FrF2 contrasts to a factorstatus <- as.factor(rep(c("current","new"),4))
contrasts(status) <- contr.FrF2(2)
contrasts(status)
# }