Don't use correlation for discrete variables; the
correlation coefficient does not vary freely between -1
and 1, it is tightly constrained by the joint probabilities of
nonzero outcomes in a rather counterintuitive way.
Please ask me off list if you don't follow this.
While I'm off-topic,
Paul -
This situation seems like an obvious candidate for a log-linear model.
See the book MASS for details. They're beyond the scope of this list.
Or try help.search(log-linear).
(and ... can you find a way to break lines when sending your email ?)
- tom blackwell - u michigan medical
