I calculated the effect size for the results of Mann-Whitney U tests but some of them are negative. I was double checking the formula and how to do it and I noticed that some of them reported a positive effect size despite the formula (by doing it myself) gave a negative effect size.

So, my question is, when you do the formula for the effect size, should you use a negatize/positive Z or should I just use the positive value?

The formula I found is Z/sq of N.

Thank you,

Statn00b