Essay

In the health psychologist's study investigating calorie estimates and weight, describe the manual steps and values required to test the correlation coefficient by hand, including how degrees of freedom are calculated and how the final decision is reached.

Question: In the health psychologist's study investigating calorie estimates and weight, describe the manual steps and values required to test the correlation coefficient by hand, including how degrees of freedom are calculated and how the final decision is reached.

Sample answer: To test the correlation coefficient by hand for a sample of 2222 students, the researcher first calculates the degrees of freedom as df=N2df = N - 2, which equals 2020 (222=2022 - 2 = 20). Next, the researcher finds the critical value for 2020 degrees of freedom in a statistical table, which is .444.444 for a two-tailed test at an alpha level of .05.05. Finally, the researcher compares the calculated Pearson's rr (.21-.21) with this critical value. Because the calculated value is less extreme than the critical value, the researcher retains the null hypothesis.

Key points:

  • The degrees of freedom formula is df=N2df = N - 2, yielding 2020 for a sample of 2222 students.
  • The critical value from the statistical table for a two-tailed test with df=20df = 20 is .444.444.
  • The calculated correlation coefficient is Pearson's r=.21r = -.21.
  • The calculated value is less extreme than the critical value, resulting in retaining the null hypothesis.

Rubric: The response must accurately name the sample size (2222), detail the formula and calculation for degrees of freedom (df=20df = 20), state the critical value (.444.444), mention the calculated Pearson's rr (.21-.21), and explain the comparison that leads to retaining the null hypothesis because the calculated correlation is less extreme.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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