Transcription of Chapter 206 Two-Sample T-Test
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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.
popularity of the t -test, particularly the Aspin-Welch Unequal-Variance t-test, is its robustness in the face of assumption violation. However, if an assumption is not met even approximately, the significance levels and the power of the t-test are invalidated. Unfortunately, in practice it sometimes happens that one or more assumption is not met.
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