Could some one tell me how to count a U test? I can´t find it anywhere! So I know you rank the values from smallest to biggest across each sample (if that makes any sense to you) and then you count the ranks together and use the following equation: U = n(1) * n(2) + ( n(1) * [ n(2) + 1])/2 - R hope that makes sense. I do not know how to write proper eqautions. However, it is the samples n multiplied + the samples multiplied (and the other +1) and divided by 2, and finally - R, which is the sum of ranks of x(1) I think. So then you are supposed to look up on a U-test table and check if U or U(1) is smaller than the critical number, and if so then you rule out Null hypothesis that they are the same. So I am sure anyone who knows this, knows what I am talking about. So my question is about how do you get the Z value from this? My book requires it, but does not explain how to. Also online calculators (such as http://www.vassarstats.net/utest.html ) give you the z value.