Introduction
A Friedman's ANOVA compares the difference between more than two related groups, such as comparing the difference between three time-points. If your data only has two groups such as a pre/post-test you should consider the Paired-Samples t-Test.
It is considered a non-parametric test and is suitable for non-parametric data. To check if your data is parametric, please check out the dedicated guide here: Parametric or Not Guide
If your data is parametric you should consider using a One-Way Repeated-Measures ANOVA
Test Procedure
Step 1: Click Analyze > Nonparametric Tests > Legagy Dialogs > K Related Samples
Step 2: Within the "Tests for Several Related Samples" Window, move your measurements into the "Test Variables" box.
Step 3: Click "Statistics". Within the "Several Related Samples: Statisitcs", select 'Descriptives' and 'Quartiles'.
Step 5: Select Continue à OK
Results
SPSS will generate three tables, to correctly report this test we need two, the Descriptive Statistics and the Test Statistics
Descriptive Statistics
This table shows the descriptive statistics: the sample size of each group (N), the mean of each group (Mean), and the standard deviation of each group (Std. Deviation), best practice is to report them all.
Test Statistics
This table shows the results of the statistics test including the sample size (N), the Chi-Square statistic (Chi-Square), the degrees of freedom (df), and the p-value/significance (Asymp. Sig.).
Reporting the Results in APA Formatting
The box in purple is mandatory, and the box in green is optional - see the note below the box.
Samples were evaluated across three-time points (Week 1, Week 2, Week3). A Friedman's ANOVA indicated there was a significant effect for test score, χ2(2) = 22.76, p<.001
On average, Week 3 (Mean = 6.48, SD = 1.72) values were higher than Group B (Mean = 6.03, SD = 1.37), but lower than Group C (Mean = 5.57, SD = 1.12).
Post hoc comparisons were conducted by performing three Wilcoxon Tests.
The differences between Week 1 and Week 2 (Z = 3.03, p=.002), Week 2 and Week 3 (Z = 2.44, p=.015), and Week 1 and Week 3, (Z = 4.84, p<.001), were all considered statistically significant.
If your Freidman's ANOVA is significant you must report your Post-Hoc results, these are indicated in green. If you need help running the post hoc test check the following guide: Wilcoxon Test
