I want to compare the grades of two cohorts A and B (of unequal size). I have the grades for a certain course 1. The grades are not normally distributed. I used the following code (in R) to compare:
wilcox.test(gradesA, gradesB, paired=FALSE, conf.int=TRUE)
However, I am not sure whether cohort A was better overall than group B, so next to my own course 1:
wilcox.test(gradesA1, gradesB1, paired=FALSE, conf.int=TRUE)
I have the grades of another course (2) earlier this year. The results of this:
wilcox.test(gradesA2, gradesB2, paired=FALSE, conf.int=TRUE)
Is:
W = 616, p-value = 0.6066
Can I now just compare A1 and B1, given that the cohorts did not significantly differed on the previous course, or how can I incorporate the other courses in my comparison?
