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MASH : Maths and Stats Help

Paired Samples t-Test

Introduction

A Paired-Samples t-Test compares the means between two related groups, such as comparing the difference between pre-intervention and post-intervention test results.

It is considered a parametric test and is only suitable for parametric data. To check if your data is parametric, please check out the dedicated guide: Parametric or Not Guide (PDF)

If your data is non-parametric you should consider using a Wilcoxon Test.

 

Test Procedure

  1. Click Analyze > Compare Means > Paired-Samples T Test

  2. Within the Paired Samples t-Test box, select the two variables you wish to analyse and move to them to the Paired Variables Box using the right arrow

  3. Select OK

 

Results

SPSS will generate three tables, for this test we need two, the Paired Samples Statistics and the Paired Samples Test.

 

Paired Samples Statistics

This table shows a selection of 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.

Paired Samples Test

This table shows the specific test results including the t-statistic (t), the degrees of freedom (df) the two-tailed significance or p-value (Two-Sided p), and the 95% Confidence Interval (95% Confidence Interval of the Difference).

Reporting the Results in APA Formatting

Students’ test results were compared before and after the intervention. On average, students performed better (Mean = 73.30, SD = 11.91) after the intervention than before (Mean = 69.00, SD = 6.64). A Paired-Samples t-Test indicated this improvement, 4.30, 95%CI [.83, 7.77] was statistically significant, t(19) = 2.60, p=.018