I have what I believe is a relatively straightforward problem. I am trying to move from SAS to R and have coded the following successfully in R: proc mixed; class name run exam; model y= a b c/s; random name; random run(name); run; as ... mod<-lme(y ~ a + b + c, random=~1|name/run, na.action=na.omit) However, when trying to introduce a correlation structure in SAS by altering the 2nd random statement to random run(name)/type=ar(1), differences then appear. I've tried coding this in R: e2<-lme(y ~ a + b + c, random=~1|name/run, correlation=corAR1(form=~1|name/run), na.action=na.omit) and the model runs fine, however the results are very different to what seems sensible to me and what SAS gives. I have attached the data if anyone wants to have a play with it, but I suspect it's my coding that's at fault. I've been using Pinheiro and Bates to get this far, but seem to have hit a wall here. Any help would be much appreciated, Paul
ar(1)
1 message · Paul Chatfield