I have x variables describing water properties that I want to correlate to water pollution (Y). Data are from different water utilities with repeated measurements with irregular time intervals. I don’t expect any linear time effect on Y in the long run (the sampling were done for more than one year) but I would like model the correlation between the repeated measurements within each water utility. Is this the SAS syntax to accomplish this? Proc Mixed Data=water_qual; class water_util; Model y = x1 x2 x3 x4 water_util/ solution DDFM=kr; Random days / Subject=water_util type=un solution; Run; Another problem I have is that Y is left-censored. I can't find any mixed model repeated measurement that takes censored data into account. Anyone has suggestion? If the Null Model Likelihood Ratio Test for the model above (for the non-censored data) is close to 1 it means that it is not necessary to model the covariance structure of the data at all and I can use a tobit model (in proc lifereg) to deal with the censored data. But how to deal with the censored data if the Null Model Likelihood Ratio Test is significant? Thanks
... View more