I am doing an analysis in which I want to run the model only for two of the five cohorts that are in my datafile. I have tried the useobservation statement, but I am not sure whether I can select two cohorts. If I use the statement 'useobservation = (cohort EQ 2 AND cohort EQ 3);' I get the error that the number of observations is 0. If I use the statement 'useobservation = (cohort EQ 2 AND 3);' I do get output, but I am not sure if this is the correct way. I hope you can help me with this.