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ERIC Number: EJ933690
Record Type: Journal
Publication Date: 2010-Oct
Pages: 12
Abstractor: As Provided
Reference Count: 31
ISSN: ISSN-1531-7714
Five-Point Likert Items: t Test versus Mann-Whitney-Wilcoxon
de Winter, Joost C. F.; Dodou, Dimitra
Practical Assessment, Research & Evaluation, v15 n11 Oct 2010
Likert questionnaires are widely used in survey research, but it is unclear whether the item data should be investigated by means of parametric or nonparametric procedures. This study compared the Type I and II error rates of the "t" test versus the Mann-Whitney-Wilcoxon (MWW) for five-point Likert items. Fourteen population distributions were defined and pairs of samples were drawn from the populations and submitted to the "t" test and the "t" test on ranks, which yields the same results as MWW. The results showed that the two tests had equivalent power for most of the pairs. MWW had a power advantage when one of the samples was drawn from a skewed or peaked distribution. Strong power differences between the "t" test and MWW occurred when one of the samples was drawn from a multimodal distribution. Notably, the Type I error rate of both methods was never more than 3% above the nominal rate of 5%, even not when sample sizes were highly unequal. In conclusion, for five-point Likert items, the "t" test and MWW generally have similar power, and researchers do not have to worry about finding a difference whilst there is none in the population. (Contains 3 tables.)
Dr. Lawrence M. Rudner. e-mail:; Web site:
Publication Type: Journal Articles; Reports - Research
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A