SAS vs. WinNonlin: different sequence effect results [Software]

posted by Eva – Germany, 2008-05-06 16:04 (5627 d 01:03 ago) – Posting: # 1817
Views: 25,551

Dear all,

I have recently analysed a simple crossover bioequivalence study in SAS and detected a significant sequence effect (p=0.0425). To verify my results, I have run the same analysis using the WinNonlin Bioequivalence Wizard (WNL v5.1.1). The results of the analysis were completely identical except for the sequence effect which was not significant (p=0.0634).

The Pharsight support claims that this is due to a slightly different model used by the Bioequivalence Wizard and recommended me to read the online help on linear mixed effects modelling.
I can not follow this argumentation, because in my opinion my model specification is the same. Besides I get identical results for all other effects: both my SAS program and the BE Wizard produce the same SS, MS and DF for sequence effect, period effect, treatment effect and subject within sequence, the MSE is identical in both programs and (consequently) also the confidence limits.
The F statistics and the p-values are the same for period effect, treatment effect and subject within sequence.

I have repeated the comparison with other data with the same result, all values identical, but the F statistic of the sequence effect always lower in WNL compared to SAS.

Has any of you ever come across this discrepancy before?
I wonder if somebody could help me to find out if there is a mistake in the Bioequivalence Wizard calculation or if I am simply too stupid to model my data correctly...

Thanks in advance & kind regards,

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