A survey was conducted with customers of two gas suppliers

Question

A survey was conducted with customers of two gas suppliers - Atomic Gas and English Gas. The objective was to assess whether one group of customers spent more (in £s) on their annual gas bill than the other. Initial tests suggested the absence of normality in the dependent variable. A non-parametric test was deemed appropriate, but which do you think that the researchers should use?
A) Paired t-test
B) Mann-Whitney test
C) Wilcoxon signed-rank test
D) Independent t-test

Quizplus · Accepted Answer

The Mann-Whitney test is a non-parametric test that can be used to compare the median values of two independent groups. Since the dependent variable does not follow a normal distribution and the two groups are independent, this test is appropriate in this situation. The Wilcoxon signed-rank test is appropriate for paired data, which is not applicable in this case as the two groups are not paired. The paired t-test is also not appropriate as the dependent variable is not normally distributed. The independent t-test assumes normality and therefore is not appropriate for this situation.