Wilcoxon Test Explained

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EPS 625 – INTERMEDIATE STATISTICS WILCOXON TEST
The Wilcoxon test was developed to analyze data from studies with repeated-measures and matched-subjects designs. For a repeated-measures design, an individual is assessed on a measure on two occasions or under two conditions. Each individual is a case in the SPSS data file and has scores on two variables, the score obtained on the measure on one occasion (or under one condition) and the score obtained on the measure on a second occasion (or under a second condition). The goal of repeated-measures designs is to determine whether participants changed significantly across occasions (or conditions). For a matched-subjects design, participants are paired, typically on one or more nuisance variables, and each participant in the pair is assessed once on a measure. Each pair of participants is a case in the SPSS data file and has scores on two variables, the score obtained on the measure by one participant under one condition and the score obtained on the measure by the other participant under the other condition. The purpose of matched-subjects designs is to evaluate whether the pairs of participants differ significantly under the two conditions. For both types of studies, each case in the SPSS data file has scores on two variables (that is, paired scores). The Wilcoxon test evaluates differences between paired scores, either repeated or matched. The variables for the Wilcoxon test have multiple possible scores, with the focus on whether the median of the variables differs significantly. The Wilcoxon test can be used to analyze data from a number of different designs: 1. 2. 3. 4. Repeated-measures designs with an intervention Repeated-measures designs without an intervention Matched-subjects designs with an intervention Matched-subjects designs without an intervention

UNDERSTANDING THE WILCOXON TEST
To help understand the Wilcoxon test, we will first describe what data are being analyzed. We will look at an example...
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