Thanks Marc, However, I still don't quite understand it. In the attached example I have done the same but the x1 and x2 only have values of +/-1. (So they are the same as their 'effect coded' version you mention, right?). Now I get the parameter effects Term Estimate Std Error Intercept -5.33e-15 7.224e-8 x1 recode 4.36 5.529e-8 (The real value is 5.) x2 recode 10 7.224e-8 x1 recode*(x2 recode+0.64) 1 7.224e-8 The effect sizes delta are given as x1 recode -> 4.35404318234411 x2 recode -> 7.64426468724727 x1 recode * x2 recode -> 0.764426468724727 From you comment I would have expected the effect sizes to be the same as the parameter estimates, but they are not (not even very close in some cases). So there is something I'm doing wrong. As to the power analysis as such, the manual distinguishes indeed between "prospective" and "retrospective" power analysis.There is a note: The results provided by the LSV0.05, LSN, and AdjPower0.05 should not be used in prospective power analysis. They do not reflect the uncertainty inherent in a future study. As I far as I understood, they should not be mixed up because the there is no guarantee that scatter is the same in different studies. Is that correct or am I missing the point?
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