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Wilcoxon Tests

Wilcoxon Tests. What is the Purpose of Wilcoxon Tests?. These are nonparametric alternatives to the independent and dependent samples t-tests. Based on ordinal data. Normal distributions are not required. What is the Purpose of Wilcoxon Tests?.

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Wilcoxon Tests

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  1. Wilcoxon Tests

  2. What is the Purpose of Wilcoxon Tests? • These are nonparametric alternatives to the independent and dependent samples t-tests. • Based on ordinal data. • Normal distributions are not required.

  3. What is the Purpose of Wilcoxon Tests? • Wilcoxon Rank-Sum Test is used in place of the independent samples t (between subjects design). • Wilcoxon Matched-Pairs T Test is used in place of the dependent samples t (within subjects or matched groups design).

  4. What Are the Assumptions? • Wilcoxon Rank Sum: • Ordinal or higher level data • Independent observations • Wilcoxon Matched-Pairs T: • Ordinal or higher level data • Paired observations • Minimum N of 6

  5. How Does the Wilcoxon Rank-Sum Work? • If the scores are not already ordinal, they are ranked from lowest to highest across both groups. • The sum of ranks is calculated for each group.

  6. How Does the Wilcoxon Rank-Sum Work? • If the Ho is true, then the sum of ranks should be the same for the two groups. • W is the smaller sum of ranks (or the sum for the group expected to have the smaller sum).

  7. How Does the Wilcoxon Matched-Pairs T Work? • Difference scores are calculated for each pair of scores. • The difference scores are ranked from lowest to highest.

  8. How Does the Wilcoxon Matched-Pairs T Work? • The sum of ranks is computed separately for positive and negative difference scores. • If the Ho is true, then the sum of ranks should be the same for positive and negative. • T is the smaller sum of ranks (or the sum for the condition expected to have the smaller sum).

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