Short Answer

Explain how the degrees of freedom (df=13df = 13) were calculated in this independent-samples tt-test. Your explanation should link the final value to the sample sizes of the two groups.

Question: Explain how the degrees of freedom (df=13df = 13) were calculated in this independent-samples tt-test. Your explanation should link the final value to the sample sizes of the two groups.

Sample answer: The degrees of freedom for an independent-samples tt-test are calculated by subtracting 2 from the combined sample size (N2N - 2). Since there are 88 frequent junk food eaters and 77 rare junk food eaters, the combined sample size is 1515 (8+78 + 7). Subtracting 2 yields 1313 degrees of freedom (152=1315 - 2 = 13).

Key points:

  • Identify the group sample sizes as 88 and 77.
  • State that the total sample size is 1515.
  • Show that subtracting 2 from the total sample size (15215 - 2) yields 1313.

Rubric: The answer must explain that the degrees of freedom are calculated using the formula df=n1+n22df = n_1 + n_2 - 2, showing the addition of 88 and 77 to get 1515, and then subtracting 22 to get 1313.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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