What to use? A parametric or non-parametric test?
"Dr. Geoff Norman, one of world's leaders in medical education research methodology, has comprehensively reviewed this controversy. He provides compelling evidence, with actual examples using real and simulated data, that parametric tests not only can be used with ordinal data, such as data from Likert scales, but also that parametric tests are generally more robust than nonparametric tests. That is, parametric tests tend to give “the right answer” even when statistical assumptions—such as a normal distribution of data—are violated, even to an extreme degree.4 Thus, parametric tests are sufficiently robust to yield largely unbiased answers that are acceptably close to “the truth” when analyzing Likert scale responses"
Paper cited above is:
Sullivan GM, Artino Jr AR. Analyzing and interpreting data from Likert-type scales. J Grad Med Educ. 2013;5(4):541-2.
The original paper being referred to is:
Norman G. Likert scales, levels of measurement and the “laws” of statistics. Adv Health Sci Educ Theory Pract. 2010;15(5):625–632.