# Is it possible to compute a mean/median score for a Mann Witney test/chi square test?

#### assignbones

##### New Member
There are two groups in my study (experimental N=19 and control N =14), and I want to see if there are any differences between the groups, so I made a survey. The survey has 15 different questions, all 5-point Likert items. However, I want to combine those items into 3 different categories, because I have 5 questions for each category. Would it be ok if I computed a mean/median score over those questions for a Mann Witney U test/chi square test (depending on if my data is normally distributed or not)? If so, which one would be better, mean or median?

Another question: what measure of central tendency should I use to see if there are differences between the two groups? I believe for a Mann Witney U test it’s very common to use the median, however won’t you have problems with ties if you do this for Likert items?

#### Karabiner

##### TS Contributor
A sum score from 5 Likert items would usually be considered as interval scaled.
Therefore, you could consider using a Welch t-test, The t-test /
Welch t-test assumes normally distributed variables in each separate population, but
with n > 30 it is usually considered robust against violation of that assumption.

Or maybe you would like to treat your data as ordinal, and perform a U-test, or a median
test (the latter compares medians).

I would not recommend to use Chi², since it is for categorical variables.

With kind regards

Karabiner

#### assignbones

##### New Member
Thank you for your answer Karabiner. If I did use a U-test, would it still be valid if I use the average score of 5 likert scale items to compare the two groups?

#### Karabiner

##### TS Contributor
The U-test (or Wilcoxon rank sum test, which produces exactely the same result) does not
compare means, and does not compare medians. Therefore, your descriptive statistics and your
inferential statistics will to slightly different things. You could maybe display means and medians