I'm preparing my data to run proc MDC but kept receiving the error: "ERROR: The NCHOICE= option is not allowed when the number of choices for each individual (ID) is not the same." I don't really get what it means. Could you help me figure out what's wrong?   The original dataset (final1) is a panel transaction data that has the columns: customerid, week, brand, p1 p2 p3 p4 d1 d2 d3 d4 f1 f2 f3 f4. (P1-P4 are average price of brand 1-4 in that week, respectively. D1-4 are dummy variables showing whether that brand  is displayed in store, f1-4 are dummy variables that show whether brand 1-4 are featured in the store ads)   I used this code to prepare the data and the outcome is in the attached file:   data mergemnl(keep=pid decision mode c1 c2 c3 p d f); set final1; array pvec{4} p1 p2 p3 p4; array dvec{4} d1 d2 d3 d4; array fvec{4} f1 f2 f3 f4;  array s1{4}(1 0 0 0); array s2{4}(0 1 0 0); array s3{4}(0 0 1 0); retain pid 0; pid + 1; do i = 1 to 4; mode = i; p = pvec{i}; d = dvec{i}; f = fvec{i}; c1 = s1{i}; c2 = s2{i}; c3 = s3{i}; decision = ( brandnum = i ); output; end; run;   This is the code I used to run mdc: proc mdc data=mergemnl; model decision =c1 c2 c3 p d f / type=clogit nchoice = 4 optmethod=qn covest=hess; id pid; run; ... View more