Introduction
The Wilcoxon Signed-Rank Test is a non-parametric statistical test used to compare two related samples. This guide provides a comprehensive overview of how to perform and interpret the Wilcoxon Signed-Rank Test in SPSS, including assumptions, procedures, and APA style reporting.
Assumptions of the Wilcoxon Signed-Rank Test
- The dependent variable should be continuous or ordinal.
- The paired observations should be randomly and independently selected from the population.
- The differences between paired observations should be symmetrically distributed.
Performing the Wilcoxon Signed-Rank Test in SPSS
- Load your dataset into SPSS.
- Go to Analyze > Nonparametric Tests > Legacy Dialogs > 2 Related Samples.
- Move the two related variables into the Test Pairs list.
- Select the Wilcoxon checkbox.
- Click OK to run the test.
Example Dataset
Consider a dataset where we have measurements of the same group of individuals at two different time points. Below is a snapshot of our data:
| Participant | Time 1 | Time 2 |
|---|---|---|
| 1 | 23 | 25 |
| 2 | 21 | 22 |
| 3 | 19 | 20 |
| 4 | 18 | 19 |
| 5 | 22 | 23 |
SPSS Output and Results
After running the Wilcoxon Signed-Rank Test in SPSS, you will get the following output:
| Ranks | N | Mean Rank | Sum of Ranks |
|---|---|---|---|
| Negative Ranks | 2 | 1.50 | 3.00 |
| Positive Ranks | 3 | 3.67 | 11.00 |
| Ties | 0 | ||
| Total | 5 |
| Test Statistics | Time 2 – Time 1 |
|---|---|
| Z | -2.023 |
| Asymp. Sig. (2-tailed) | .043 |
Results Interpretation
The Wilcoxon Signed-Rank Test showed that there was a statistically significant difference in the scores between Time 1 and Time 2, Z = -2.023, p = .043.
APA Results Reporting
In APA format, you would report the results as follows:
A Wilcoxon Signed-Rank Test was conducted to determine whether there was a statistically significant difference in scores between Time 1 and Time 2. The results indicated a significant difference, Z = -2.023, p = .043.
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Conclusion
The Wilcoxon Signed-Rank Test is a valuable non-parametric method for comparing two related samples. By following this guide, you can effectively perform and interpret the Wilcoxon Signed-Rank Test in SPSS, ensuring your results are reported accurately in APA format.