Hi again! I tried the by statement and the numbers remained the same. How I put them as a third variable in the model? Because it says that can't be done.   Be sure that you understand the difference between BY variables and CLASS variables in SAS. If you want to be able to compare the effects of different months and days, they need to be class variables and part of the model. If you just want to subset the data by month and day, then use the BY statement.   ... View more