2010) at a significance level of 0.05.īased on these results, the new fuel treatment does not have a significant impact on the miles per gallon of cars. Results showed that the mean mpg was not statistically significantly different between the two groups (z = -1.279, p =. NPAR TESTS Mann-Whitney (npar.at:976): ok (0m0.016s 0m0.008s) 579. Here is an example of how to do so:Ī Mann-Whitney U test was conducted on 24 cars to determine if a new fuel treatment lead to a difference in mean miles per gallon. Lastly, we will report the results of our Mann-Whitney U test. This manual is for GNU PSPP version 1.6.2-g652517, software for statistical. We do not have sufficient evidence to say that the true mean mpg is different between the two groups. Since the p-value is not less than 0.05, we fail to reject the null hypothesis. The most important numbers in the output are the Z test statistic and the Asymptotic 2-tailed p-value: Once you click OK, the results of the Mann-Whitney U Test will be displayed: Make sure the box next to Mann-Whitney U is checked. Then click OK. Click on Define Groups and define Group 1 as the rows with value 0 and define Group 2 as the rows with value 1. Simple tutorial with downloadable practice data file. Step 2: Fill in the necessary values to perform the test.ĭrag mpg into the box labelled Test Variable List and group into the box labelled Grouping Variable. SPSS Mann-Whitney test evaluates if two groups of cases have equal means on some outcome variable. Step 1: Select the Mann-Whitney U Test option.Ĭlick the Analyze tab, then Nonparametric Tests, then Legacy Dialogs, then 2 Independent Samples: Perform the following steps to conduct a Mann-Whitney U test in SPSS. Since the sample sizes are small and the researchers suspect that the sample distributions are not normally distributed, they decided to perform a Mann-Whitney U test to determine if there is a statistically significant difference in mpg between the two groups. The following screenshot shows the mpg for each car along with the group they belong to (0 = no fuel treatment, 1 = fuel treatment): To test this, they conduct an experiment in which they measure the mpg of 12 cars with the fuel treatment and 12 cars without it. In statistics, the MannWhitney U test (also called the MannWhitneyWilcoxon (MWW/MWU), Wilcoxon rank-sum test, or WilcoxonMannWhitney test) is a nonparametric test of the null hypothesis that, for randomly selected values X and Y from two populations, the probability of X being greater than Y is equal to the probability of Y being greater than X. Researchers want to know if a fuel treatment leads to a change in the average mpg of a car. This tutorial explains how to perform a Mann-Whitney U test in SPSS. It is considered to be the nonparametric equivalent to the two sample t-test. A Mann-Whitney U test (sometimes called the Wilcoxon rank-sum test) is used to compare the differences between two samples when the sample distributions are not normally distributed and the sample sizes are small (n <30).
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