SPSS Tutorial: Dependent (paired) samples t test

In this tutorial I explain the purpose and assumptions of the dependent (or paired) samples t-test. I work through an example using fictitious data in SPSS v23.

Paired (or dependent) samples t-test is a statistical technique that is used to compare two population (sample) means in the case of two samples that are correlated.  Paired sample t-test is used in ‘before-after’ studies, when the samples are the matched pairs, or when it is a case-control study.

A dependent t-test is an example of a "within-subjects" or "repeated-measures" statistical test. This indicates that the same subjects are tested more than once. Thus, in the dependent t-test, "related groups" indicates that the same subjects are present in both groups. The reason that it is possible to have the same subjects in each group is because each subject has been measured on two occasions on the same dependent variable.

Formula for paired samples t-test:

Assumptions:

1. Only the matched pairs can be used to perform the test.

2. Normal distributions are assumed.

3. The variance of two samples is equal.

4. Cases must be independent of each other.

SPSS Guide: