Hi Jerrome,

the assumptions that the data follow a normal distribution will be violated if you consider ordinal data. Thus, a typical paired t-test would at best lack sensitivity, and at in the worst case provide biased estimates. However, there are non-parametric versions of the t-test which do not depend on the assumption of normality, e.g. the signed-rank test (= U-test). It is designed for paired comparisons on non-normal data.

Best