Graziano and Raulin (8th ed)Graziano & Raulin
Research Methods (8th edition)

Correlated Samples t-test

The correlated t-test is used whenever we have two groups in either a within-subjects or a matched subjects design. For the purpose of illustration, we will use the data that appears in Table 11.1 of the text. This table presents the data for three groups, but we will act as if there were only two groups (10 distracters and 15 distracters) to illustrate the correlated samples t-test.

The file Table_11-1.sav is on website and can be downloaded to your computer. To open the file containing the data from Table 11.1, we use the File menu and select the Open option.  This screen shows the data set we will be working with. We have already named and formatted each of the variables for you. 

To run a correlated samples t-test, you select the Analyze menu, the Compare Means submenu, and the Paired Samples T Test option, which will give you this screen. You need to highlight the two variables (in this case, ten and fifteen) and move them into the right box using the arrow between the boxes as shown in this screen. Note that you can ONLY move the two variables as a pair. You cannot move them one variable at a time. Clicking on OK will then run the analysis giving you the results shown in this screen.

Note again, that for the data shown in Table 11.1 of the text (three conditions in a within-subjects design), the appropriate analysis is a repeated measures ANOVA. We used only two of the three groups to illustrate the correlated samples t-test, even though this would not be the optimal data analysis choice. We did this solely for the purpose of illustrating how you would go about computing a paired samples t-test.

Animations

We have prepared an animation that will walk you through this procedure. To run an animation, simply click on the title of the animation in the table below. 

Note that we do not recommend that you try to run the animations if you have a slow connection, such as a dial-up connection. You will find that the animations take forever to load with a slow connection.

Running a Correlated Samples t-test