The missing piece is why there are two clusters. There is most likely a two-level factor distinguishing the groups that was not included in the model. It might not even have been measured and now you need to find it.
Rich ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
