Dear Allin I replicate the CEL example for DPM open CEL.gdt ngd = n + 0.05 ly = log(y) linv = log(s) lngd = log(ngd) # take out time means loop i=1..8 --quiet smpl (time == i) --restrict --replace ly -= mean(ly) linv -= mean(linv) lngd -= mean(lngd) endloop smpl --full list X = linv lngd # 1-step GMM-DIF dpanel 1 ; ly X ; GMM(linv,2,99 I had no problem with the implementation however I encounter a problem: apparently the time-demeaned series do not have missing values but the original ones had. Could you help me? Sincerely -- João Sousa Andrade