03-25-2012 10:14 AM
While using PROC NLMIXED or GEE is there a specific way the clustering variable should be coded.
Does coding effects the results. For instance say I have subject=PHYSICIAN in my PROC NLMIXED option or repeated subject=PHYSICIAN in PROC GEE will it effect my results or will it create issues with convergence if I code PHYSICIAN as (1,2,3,4) or PHYSICIAN as (64055, 65471,56432).
If it does effect then how can I change the coding scheme for a variable in SAS. As currently my PHYSICIAN is coded with 5 digit numeric codes (eg physician A has code 64055, physican B has code 65275 and so on). There are 58 physicians (clusters) and the cluster size (number of patients being treated by each physician) varies from 1 to 39.
Looking forward for your ocmments and suggesitons.
03-26-2012 07:50 AM
So long as the clustering variable is explicitly included in the CLASS statement, it should be OK. I worry somewhat about the 'repeated' statement, but I believe you will be using PHYSICIAN as in SUBJECT=PHYSICIAN part. If not, then careful consideration needs to be made as to the possible covariance structures and the effect of coding on them.