Comments (15) Description of the problem with effect coding
When you have a categorical independent variable with more than 2 levels, you need to define it with a CLASS statement. In PROC GLM the default coding for this is dummy coding. In PROC LOGISTIC, it’s effect coding. To me, effect coding is quite unnatural.
Continue reading 'PROC LOGISTIC: Reference coding and effect coding'»
The problem of coding 0 and 1 in PROC LOGISTIC
PROC LOGISTIC can be used to run logistic regression on a dichotomous dependent variable. Often, these are coded 0 and 1, with 0 for `no’ or the equivalent, and 1 for `yes’ or the equivalent. In this case, we are usually interested in modeling the probability of a ‘yes’. However, by default, SAS models the probability of a 0 (which would be a `no’).
Whenever you run a SAS program, you should look at the log file. In fact, I have set up keys on my SAS sessions so that when I hit F8, it submits and then goes to the log. One possible exception is when you are running the exact same program on different data, but, even here, I check the log. There might be something wrong with the data.
So, check the log! You’ll save yourself time and anguish and errors in the long run.
To set up your keys, press F9 and then edit the commands you see there.
