A Z value is extracted from the wilcox_test
function in the
coin package. r is calculated as Z divided by
square root of the total observations.
Currently, the function makes no provisions for NA
values in the data. It is recommended that NA
s be removed
beforehand.
When the data in the first group are greater than
in the second group, r is positive.
When the data in the second group are greater than
in the first group, r is negative.
Be cautious with this interpretation, as R will alphabetize
groups if g
is not already a factor.
When r is close to extremes,
or with small counts in some cells,
the confidence intervals
determined by this
method may not be reliable, or the procedure may fail.