Dear Jesper, thanks again. I've run design_ttest2 design 6 6 to create my design files. In the description it reads "for the two-group unpaired t-test case". So I never used the glm gui. And these 2 groups are different, I mean they are genetically different, therefore I thought this setup should be right. But I am not sure if the output would be 2-tailed or not. I've assumed so, since the software cannot assume in which direction it would go, and because of the output (negative and positive values), I assumed that it's 2-tailed. So my only uncertainty is currently if the output of design_ttest2 design 6 6 would be 2-tailed or not. Thanks again for efforts. Cheers, Torsten