Chapter 206 Two-Sample T-Test

NCSS Statistical Software 206-1 NCSS, LLC. All Rights Reserved. Chapter 206 Two-Sample T-Test Introduction This procedure provides several reports for the comparison of two continuous-data distributions, including confidence intervals for the difference in means, Two-Sample t- tests , the z-test, the randomization test, the Mann-Whitney U (or Wilcoxon Rank-Sum) nonparametric test, and the Kolmogorov-Smirnov test. tests of assumptions and plots are also available in this procedure. The data for this procedure can be contained in two variables (columns) or in one variable indexed by a second (grouping) variable. Research Questions A common task in research is to compare two populations or groups. Researchers may wish to compare the income level of two regions, the nitrogen content of two lakes, or the effectiveness of two drugs. An initial question that arises is what aspects (parameters) of the populations should be compared. We might consider comparing the averages, the medians, the standard deviations, the distributional shapes, or maximum values.

compared to the other (as there is in the paired t -test). 5. Both samples are simple random samples from their respective populations. Each individual in the population has an equal probability of being selected in the sample. Mann-Whitney U Test Assumptions The assumptions of the Mann- Whitney U test are: 1.

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