one follow up:
Like lmr() from the Design package, `gee' doesn't like it when you give it
dummies that create collinearity. run glm() first, and see what it dropped to avoid
collinearity. Then, drop those from your specification. Run this using gee(), and use
the id=`` for specifying what you want to cluster on.
--
ERIC LIN
Technology and Operations Management
Harvard Business School
Boston, MA 02163
elin at
hbs.edu