I am very curious as to why the OP would want to do a non-parametric test. Are the response variables really non-normally distributed? If the response variable is a concentration, perhaps a lognormal distribution can be assumed, and the GLIMMIX approach appropriately modified with a dist= option. On the other hand, if there is a problem with responses being above or below limit of quantitation for the assay, I can understand wanting to move to a nonparametric test. However, if this is not the case, the detectable difference for the nonparametric test will be much larger than for the parametric test. And of course, once those plots are examined, it may be really obvious why a nonparametric approach would be needed. Steve Denham
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