we have an experiment with 3 within-subject factors: SOA(4 levels), Congruency (2 levels) and Visibility Rating (4 levels). RT is our dependent variable. Because we receive Visibility Rating score from participants for each trial, we have a number of missing values for some conditions/participants, for example, a participant can never use Visibility rating 1, so we miss all SOA*Congruency conditions for visibility rating 1. (Yes, we still want to use Visibility rating in the model, though technically it is not a regular independent variable). Therefor, we want to used Mixed models for repeated measures design. We did found a variety of codes for similar designs (but only for 2 within- and 1 between-subject factors), we also noticed that people use different syntax in proc Mixed. Could you, please, help us and suggest an appropriate code for our particular case in SAS? We will greatly appreciate any feedback. Dina.