How do I perform a nonparametric test for Likert data?

[#1]

Dear experts, 

Pardon my novice question. I am new to JMP Pro (14.2) and to statistics. I have three survey questions, each on a 5 point Likert scale, which were answered by two groups, group A and group B. There is a different N between the groups. I would like to assess for any difference, on each question between the two groups (e.g. question 1 responses from A compared to B). 

I had planned on a Mann-Whitney U test. I put in Likert responses in as ordinal (see attached image). When I Analyze Y by X, I do not see the nonparametric option. I only see nonparametric if I change the Data Type to continuous.  

I am able to complete a Mann-Whitney U in JMP Pro? Do have to use the Wilcoxon test? If so, is it ok to consider the Likert data interval, not ordinal, in this case? 

Cordially, 

Jared 

[#2 · Accepted solution]

Nonparametric techniques work on ranked data. The measurements are usually continuous, then ranking is performed and the procedure would be performed on the rankings. That is why JMP is expecting a continuous response, not ordinal. Even if the data were already ranked, JMP would "re-rank" resulting in the same data. 

If you truly want to use a nonparametric technique, make the column continuous. Then you can perform the technique. Keep in mind that Likert data does not necessarily require a nonparametric technique, but this is a point of discussion among statisticians.