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Department of Psychology

PSY2003 Statistics for Psychology

Spring Semester 2022-23

Assignment 3 (Due date: 12 Apr 2023)

Instructions for doing home assignment:

Ø Write down your name and student ID clearly on your assignment (A4-sized paper).

Ø Do NOT use SPSS or Excel unless you are told to do so.

Ø Do NOT directly print out the SPSS output. Attach those useful ones ONLY.

Ø Please show the steps of computation clearly.

Ø Please submit a hardcopy in class.

Ø Any late submission of assignment without any justified reason will be penalized.

Ø If you have any question about the assignment, please contact me by email ([email protected]).

Question 1

It appears that there is some truth to the old adage “That which doesn’t kill us makes us stronger.” In an attempt to evaluate this old adage, a researcher surveys a group of college students to determine the negative life events that they experienced in the past 5 years and their current feeling of well-being. For n₁= 18 participants with 2 or fewer negative experiences, the average well-being score is  = 42 with  = 23, and for n₂ = 16 participants with 5 to 10 negative experiences the average scores is  = 48 with  = 25.

a. Based on this old adage, state the statistical hypotheses H₀ and H₁ for this study.

b. Test the hypotheses in part (a) using an appropriate test with α = .01.

c. Compute the 95% confidence interval for the difference between means, μ₂ – μ₁.

d. How would you comment on the truth of this adage if you were the researcher?

Question 2

A researcher for a cereal company wanted to demonstrate the health benefits of eating oatmeal. A sample of 9 volunteers was obtained and each participant ate a fixed diet without any oatmeal for 30 days. At the end of the 30-day period, cholesterol was measured for each individual. Then the participants began a second 30-day period in which they repeated exactly the same diet except that they added 2 cups of oatmeal each day. After the second 30-day period, cholesterol levels were measured again. The following table summarizes the data collected in this study:

a. Are the data sufficient to indicate a significant change in cholesterol level? Test with α = .05.

b. Compute r², the percentage of variance accounted for by the treatment, to measure the size of the treatment.

Question 3

Cognitive behavior therapy and family therapy are two of the treatments for anorexia. A researcher has done a study on the two treatments for anorexia in young girls. Before the treatment, the researcher measured the body weight of each patient. After that, the patient either received cognitive behavior therapy or family therapy. After the treatment, the researcher measured the body weight of each patient again. Please use SPSS for this question. The dataset “assignment3-3.sav” for this study can be downloaded from Moodle.

a. Run an appropriate analysis to test if there is any significant difference in the weight of the patients between the two therapy groups before the treatment. Use α = .05. Copy the relevant SPSS output and report the results using your own words.

b. Run an appropriate analysis to test if there is any significant difference in the weight of the patient before and after the treatment in the cognitive behavior therapy group. Use α = .05. Copy the relevant SPSS output and report the result using your own words.

c. Compute the Cohen’s d to measure the effect size of cognitive behavior therapy.

d. Run an appropriate analysis to test if there is any significant difference in the weight of the patient before and after the treatment in the family therapy group. Use α = .05. Copy the relevant SPSS output and report the result using your own words.

e. Compute the Cohen’s d to measure the effect size of family therapy.