Case Study

Based on the case context, determine whether the psychologist should reject the null hypothesis. Explain your decision by referencing the critical values, the distribution tails, and the resulting pp-value.

Case context: A psychologist studies how sleep deprivation affects cognitive control. They conduct a two-tailed test with 2424 degrees of freedom and set their alpha level to .05.05, which establishes critical values at 2.0642.064 and 2.064-2.064. The analysis yields a computed tt score of 2.502.50.

Question: Based on the case context, determine whether the psychologist should reject the null hypothesis. Explain your decision by referencing the critical values, the distribution tails, and the resulting pp-value.

Sample answer: The psychologist should reject the null hypothesis. The computed tt score of 2.502.50 is greater than the upper critical value of 2.0642.064, placing it within the highest 2.5%2.5\% of the distribution. Because the score falls into this extreme outer region, the resulting pp-value is less than .05.05, which provides sufficient statistical evidence to reject the null hypothesis.

Key points:

  • The psychologist should reject the null hypothesis.
  • The computed tt score of 2.502.50 exceeds the upper critical value of 2.0642.064.
  • The computed score falls in the highest 2.5%2.5\% of the distribution.
  • The resulting pp-value is less than .05.05, indicating sufficient statistical evidence.

Rubric: The response must indicate that the psychologist rejects the null hypothesis, explain that the computed tt score of 2.502.50 is greater than the critical value of 2.0642.064, mention that this score falls in the highest 2.5%2.5\% region, and state that the resulting pp-value is less than .05.05.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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