The degrees of freedom for a t test of the difference of population means in a matched pairs experiment is samples is n₁ - 1, because n₁ = n₂.

Question

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In a matched pairs experiment, each subject is paired with another subject, and the difference between the two measurements is calculated. Therefore, there are only n pairs of data, not 2n independent observations. As a result, the degrees of freedom for a t-test in a matched pairs experiment is n-1, not 2n-2. Therefore, n₁ = n₂, and the correct degrees of freedom is n-1.

The Degrees of Freedom for a T Test of the Difference