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The Repeated Measures ANOVA is similar to the One-Way ANOVA, but is used when comparing groups made up of the same people. In technical terms, each participant experiences each level of the independent variable, rather than a typical one-way ANOVA where each participant belongs to only one group.

**Assumptions**

- One continuous (interval or ratio) dependent variable and one categorical (nominal or ordinal) independent variables with two or more dependent groups.
- No significant outliers - can be assessed using boxplots, scatterplots, and other methods
- Dependent variable is approximately normally distributed
*for each level*of the independent variable - Sphericity - tested using Mauchly's test of sphericity

**Running One-Way ANOVA in SPSS**

- Analyze > General Linear Model > Repeated Measures
- Edit the Within-Subject Factor Name (default "factor1") to something more meaningful (i.e. IV name)
- Enter the number of levels for that factor. Click "Add".
- Edit the "Measure Name" to something more meaningful (i.e. DV name). Click "Add".
- Click "Define" to move to the next window.
- Transfer the variable for each level of the IV into their respective places in the Within-Subjects Variables box.
- You may select additional output, such as descriptive statistics, using the Options button
- You may include univariate graphs using the Plots button
- You may include estimated marginal means using the EM Means button
- You can select your post hoc test(s) using the Post Hoc button
- Click OK to run the analysis

**Interpreting the Output**

- Descriptives (if you opted to include them)
- provides means and standard deviations based on combinations of levels of the IVs

- Tests of Within-Subjects Effects
- provides the results of the statistical tests
- test statistic = F-ratio
- associated probability = Sig.
- which value you report depends on the results of your sphericity test

- used to make a decision about the null hypothesis

- provides the results of the statistical tests
- Pairwise Comparisons
- provides the results of the post hoc analysis
- allows you to determine exactly which groups are significantly different than each other
- compare the Sig. to your level of significance (i.e. .05)

**Reporting Results in APA Style**

A Repeated Measures ANOVA determined that word recall performance varied significantly across points in time (*F*(1.382, 21.813) = 25.21, *p* < .01). A post hoc analysis showed that while there was not a significant difference between recall performance at 12 hours (*M* = 32, *SD* = 8) and 24 hours (*M* = 28, *SD = 7*), recall performance at 48 hours (*M* = 12, *SD* = 3) was significantly lower than the previous checks.

- Last Updated: Oct 31, 2024 9:47 AM
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