Chapter 206 Two-Sample T-Test

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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.

The typical comparison of two distributions is the comparison of means. If we can safely make the assumption of the data in each group following a normal distribution, we can use a two-sample t-test to compare the means of random samples drawn from these two populations. If these assumptions are severely violated, the nonparametric

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