Essay

A clinical psychology researcher wants to test whether an intervention reduces anxiety scores below the national average. The hypothetical population mean anxiety score is μ0=50\mu_0 = 50. After the intervention, a sample of N=25N = 25 participants has a mean anxiety score of M=44M = 44 with a sample standard deviation of SD=10SD = 10. Using the one-sample tt-test formula t=Mμ0SDNt = \frac{M - \mu_0}{\frac{SD}{\sqrt{N}}}, calculate the tt statistic. Show your work step-by-step and explain how the numerator and the denominator each contribute to the final calculated value.

Question: A clinical psychology researcher wants to test whether an intervention reduces anxiety scores below the national average. The hypothetical population mean anxiety score is μ0=50\mu_0 = 50. After the intervention, a sample of N=25N = 25 participants has a mean anxiety score of M=44M = 44 with a sample standard deviation of SD=10SD = 10. Using the one-sample tt-test formula t=Mμ0SDNt = \frac{M - \mu_0}{\frac{SD}{\sqrt{N}}}, calculate the tt statistic. Show your work step-by-step and explain how the numerator and the denominator each contribute to the final calculated value.

Sample answer: First, I calculate the numerator: Mμ0=4450=6M - \mu_0 = 44 - 50 = -6. This represents the difference between our sample mean and the hypothetical population mean. Next, I calculate the denominator, which represents the standard error: SDN=1025=105=2\frac{SD}{\sqrt{N}} = \frac{10}{\sqrt{25}} = \frac{10}{5} = 2. Finally, I divide the numerator by the denominator to get the tt statistic: t=62=3.00t = \frac{-6}{2} = -3.00. The numerator shows the absolute difference between the sample and the population, while the denominator accounts for the variability and sample size.

Key points:

  • Calculates the numerator as 44 - 50 = -6.
  • Calculates the denominator as 10 / 5 = 2.
  • Calculates the final t-statistic as -6 / 2 = -3.00.
  • Explains the numerator reflects the absolute difference from the hypothetical population mean.
  • Explains the denominator reflects the standard error or variability relative to the sample size.

Rubric: The essay should correctly calculate the numerator (-6), the denominator (2), and the final t-statistic (-3). It should also briefly explain that the numerator measures the mean difference and the denominator measures expected variability based on standard deviation and sample size.

0

1

Updated 2026-05-27

Contributors are:

Who are from:

Tags

KPU

Research Methods in Psychology - 4th American Edition @ KPU

Related