# MASH : Maths and Stats Help

### Paired Samples t-Test, using Jamovi

#### 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.

If you have three or more groups consider using a One-way Repeated Measures ANOVA.

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. To carry out a paired t-test, you will need to identify the two columns of data to use, one column for the first part of the pair (e.g. pre-intervention) and another for the second part of the pair (e.g. post-intervention). The pairings of data are across the rows.

2. Select the "T-Test" option, drop down the menu and select "Paired Samples T-Test":

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3. The Paired Samples T-Tests options will open. Using the arrow button, move the two variable across to the "Paired Variables" box. Look though the options on this view for additional information you may want, here we have selected the addition of "Descriptives", "Mean difference" with "Confidence interval", to get the basic data for the write up. Your results will appear to the right of the options box, and will update as you tick or untick options.

#### Results

Jamovi produces the results as you add variables and tick options. If you have results that you don't need or find you have not selected all that you want, you can come back to the menu at any point to change your selection.

For this t-test, the results are given in two tables; a "Paired Samples T-Test" table and a "Descriptives" table, these are produced in APA style formatting.

##### Descriptives

This table shows a selection of descriptive statistics: the sample size (N), the mean of each score (Mean), the median of each score (Median), the standard deviations (SD) and the standard errors (SE). Typically the N, Mean and SD or SE are reported.

##### Paired Samples Test

This table shows the specific test results including the t-statistic (statistic), the degrees of freedom (df), p-value (p), the mean difference between the scores (Mean difference) and the 95% Confidence Intervals (95% Confidence Interval, lower and upper).

## Reporting the Results in APA Formatting

Here is an example of how this could be reported, with the numbers in APA format:

Students’ test results were compared before and after the intervention. On average, students performed better after the intervention (M = 73.30, SD = 11.91),  than before (= 69.00, SD = 6.65). A Paired-Samples t-Test indicated this mean difference of -4.30, 95%CI [-7.77,-0.83], was a statistically significant difference, (19) = -2.60, = .018.