Short Answer

An educational psychologist is analyzing test scores for a class of 30 students (N=30N = 30) using a one-sample tt-test. Apply the formula for degrees of freedom to determine the dfdf value they must report, and state what this value specifies about the statistical model.

Question: An educational psychologist is analyzing test scores for a class of 30 students (N=30N = 30) using a one-sample tt-test. Apply the formula for degrees of freedom to determine the dfdf value they must report, and state what this value specifies about the statistical model.

Sample answer: The researcher calculates the degrees of freedom as df=301=29df = 30 - 1 = 29. This value of 2929 specifies the exact shape of the tt distribution model used for the hypothesis test.

Key points:

  • Apply the formula df=N1df = N - 1 to a sample of N=30N = 30.
  • Calculate the degrees of freedom as df=29df = 29.
  • The degrees of freedom value defines the shape of the tt distribution.

Rubric: The answer must show the calculation df=301=29df = 30 - 1 = 29 and mention that this value determines the exact shape of the tt distribution.

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Updated 2026-05-26

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Research Methods in Psychology - 4th American Edition @ KPU

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