# Comparisons on nonparametic, unequal variance data

I am trying to compare financial investment of 2 groups, however, my data is not normally distributed AND has unequal variance between the two groups. I thought of using the Mann-Whitney on SPSS but I read that to use the Mann-Whitney data must have equal variance, is there any exception to this rule? I have decent sample sizes with my smallest sample size being 85, would this large sample size allow me to use a t-test with unequal variance?

Any help would be appreciated.

• Where did you read that the Mann-Whitney U-test requires equal variance? Can you site the source and quote where this was claimed? Aug 12, 2016 at 1:13
• Data are neither parametric nor nonparametric; those are adjectives that apply to models or techniques. If you mean "not normally distributed" that's not at all the same thing as "nonparametric" and similarly "parametric" is not at all the same thing as "normally distributed" -- one can fit parametric non-normal models and correspondingly, one can happily use nonparametric procedures on data drawn from normal distributions. Please amend your post to more clearly express the actual situation. Aug 12, 2016 at 3:29
• There's no such rule. If you want to make a particular kind of interpretation of the results, you might assume equal shapes and equal variance (e.g. if you explicitly want to be able to interpret rejection as a mean-shift). But the test has no such requirement. Who says this is a rule? Can we have the context? Aug 12, 2016 at 3:31
• Hi Gung, I do not have the original source, however, here is a powerpoint I got off of the University of Ohio statistics site which has the same information; ohio.edu/plantbio/staff/mccarthy/quantmet/lectures/Nonparm.pdf ; also by nonparametric I meant not normally distributed. Aug 13, 2016 at 17:09
• @E.Brogdon, the information in that document is at best misleading. You do not need identical distributions, unless you want to interpret the result as showing the means differ. (Note that, for me to be 'pinged', you need to put "@" before my username.) Aug 13, 2016 at 17:15