The Wilcoxon signed rank test requires interval scaled variables, yours are ordinal.

You can use the *sign* *test* for dependent ordinal variables.

With kind regards

Karabiner

Hi Karabiner,

If you assume that the null assumption of the Wilcoxon signed-rank test is:

H0: The probability of the difference is greater than zero equals the probability of the difference is less than zero

Then I assume ordinal data is okay.

I don't think that only the ratio scale is required, I assume any continuous data will do the job.

The only problem with the ordinal data is the ties (equal values), the traditional exact test assumes there are no ties.

For this problem, you may use the correction for the ties, but with z approximation.

I also read that there are exact calculations with ties, not sure if yet in any of the main software.

Clearly, only 4 options for a question has many ties.

When you use the sign test you loose knowledge since there is no difference between "Definitely not" and "Probably not"

I would only guess that the Wilcoxon signed-rank will have a better test power.

If the labels would be 1,2,3,4 instead of the ordinal "Definitely not", "Probably not",...

we may say it is an interval scale?

My personal opinion is that there is no significant "psychological" difference between the two options.