期刊名称：Practical Assessment, Research and Evaluation
印刷版ISSN：1531-7714
电子版ISSN：1531-7714
出版年度：2010
卷号：15
出版社：ERIC: Clearinghouse On Assessment and Evaluation
摘要：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
