Evaluating Types of Therapy & Results Reported in a Quantitative Study
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1. Foa, Rothbaum, Riggs, and Murdock (1991) conducted a study evaluating four different types of therapy for rape victims. The Stress Inoculation Therapy (SIT) group received instructions on coping with stress. The Prolonged Exposure (PE) group went over the events in their minds repeatedly. The Supportive Counseling (SC) group were taught a general problem-solving technique. Finally, the Waiting List (WL) control group received no therapy. Data with the same characteristics as theirs follow, where the dependent variable was the severity rating of a series of symptoms.
Group n Mean S.D.
SIT 14 11.07 3.95
PE 10 15.40 11.12
SC 11 18.09 7.13
WL 10 19.50 7.11
a) The analysis of variance (ANOVA) was run, and the results are in the following table. Draw whatever conclusions are warranted. Interpret what the conclusions mean.
Source df SS MS F
Treatment 3 507.840 169.280 3.04*
Error 41 2279.067 55.587
Total 44 2786.907
* p < .05
b) The Bonferroni test was run to compare the WL group with each of the other three groups. The results are in the following table. What would you conclude? How does this compare to the answer to part a?
WL versus SIT WL versus PE WL versus SC
t = 2.73 t = 1.23 t = 0.433
The critical value of the Bonferroni test is 2.50.
2. Examine the following results reported in a quantitative study:
"The scores varied for band members (M=3.5), choir members (M=3.9), and for student athletes (M=5.4) for attitudes toward engaging in school activities during the 3-5 p.m. period of time. A comparison of the groups, at an alpha of .05, showed a statistically significant difference among the three groups, F (3, 8) = 9.87, p = .031, effect size = .91 SD."
As you examine this statement, you conclude: (state whether the statements below are NO or YES).
The null hypothesis was rejected.
The level of significance showed a probability of rejecting set at 5 out of 100 times.
The statistical test used was a t-test.
The magnitude of differences among the groups was over one standard deviation.
Band members differed significantly from student athletes in their attitudes.
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The expert evaluates the types of therapy and results reported in a quantitative study.
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1. a) Since P value is smaller than 0.05, we could reject the null hypothesis and conclude that at least two groups have significant difference in the mean severity rating for a series of symptoms.
b) Since 2.73>2.50, we could reject null hypothesis and conclude that WL and SIT have significant difference in the mean ...
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