There are two laboratories measuring identical samples. One of the lab's data is non-normal, therefore I am looking for a non-parametric test.
After comparing overall differences in the dependent variable (continuous) using Wilcoxon Mann-Whitney, I wish to test for differences between labs based on a third variable.
There are a number of third variables that I wish to test for, and some of them are categorical (2 levels, and 3 levels), and another is ordinal (by month).
Which test would be appropriate? I read about the van Elteren test, but the SAS output did not make sense.
Thanks in advance!