[Gretl-users] DPANEL user-guide a question

Hi there, I have a question concerning p.146 in the user-guide: Is this correct? "dz = diff(z) dpanel 1 ; y dz dpanel 1 ; y dz ; GMM(*z*,0,0)" Or should it be dpanel 1 ; y dz ; GMM(*dz*,0,0) It the first one is right, then it's because the differences of the instruments are computed after using them as instruments, while in the latter specification they are not altered any more. I tried both variants in a few examples and found that the results of dpanel 1 ; y dz dpanel 1 ; y dz ; GMM(*dz*,0,0) are very similar, but not the same, while dpanel 1 ; y dz dpanel 1 ; y dz ; GMM(*z*,0,0) gives 'totally' different coeffietints and especially s.e. for dz. I think it's quite crucial to understand this methodology and hence I'd be happy for clarification. Cheers Leon