The degrees of freedom for the related-samples t test are the number of pairs of participants minus one and not always the total number of participants minus one.

Question

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The degrees of freedom for the related-samples t test are determined by the number of pairs of participants, since each pair provides one piece of information (the difference between their scores) that contributes to the test statistic. Therefore, the degrees of freedom are equal to the number of pairs minus one. This is different from the independent-samples t test, where the degrees of freedom are based on the total number of participants minus two.

The Degrees of Freedom for the Related-Samples T Test Are