> What is the meaning of offset? As in glm() an offset is a variable on the right hand side of the equation that is a fixed part of the predictor. When doing linear regression, or rpart with continuous Y, there is no need for an offset; adding +offset(x3) on the right hand side of the equation gives the same result as (y -x3) on the left. But when y is a classification variable this is not so. I am blanking on the reference, but there has been a paper in the last 2 years that did this nicely. The response was a yes/no variable and there were both continuous predictors like age that were best handled with a logistic model, and genotype ones for which rpart was desired. The author fit the logistic and used the resulting linear predictor as on offset in rpart, then used the genotype classes found in rpart as an offset in the logistic, ...., back and forth, with convergence in 2-3 iterations.
Terry Therneau ______________________________________________ R-help@r-project.org 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.
