Question

A counseling psychologist is interested in three types of therapy for modifying snake phobia. However, she does not believe that one type of therapy is necessarily best for everyone; instead, the best type might depend on the severity of the phobia. Undergraduate students enrolled in an introductory psychology course who volunteer are given the Fear Schedule Survey (FSS) to screen out those who show no fear of snakes. Those displaying some fear are classified as either mildly, moderately, or severely phobic on the basis of the FSS. One third of subjects within each level of severity are randomly assigned to a treatment condition (treat): systematic desensitization (des), implosive therapy (impl), or insight therapy (insig). After the end of treatment, each participant completes the Behavioral Avoidance Test (high scores indicate a better outcome, less phobic).

1. Which of the following best describes the study design being used in this study?

a. 1 between and 1 within subjects factorial ANOVA. b. 2x3 between subjects factorial ANOVA. c. 3x3 between subjects factorial ANOVA. d. 3x3 within subjects factorial ANOVA

2. The F test for the factor treatment (treat) would be described as which type of test?

Anova Table

Response: test

Sum Sq Df F value Pr(>F)   

treat 51.511 2 4.0173 0.026616 *

severity 235.244 2 18.3466 3.21e-06 ***

treat:severity 112.356 4 4.3813 0.005468 **

Residuals      230.800 36                    

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Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

a. Test of main effect. b. Post-hoc test. c. Multiple comparison test. d. Test of interaction effect

3. The mean square (MS) values have not been included in the output, what is the MS value for the severity factor?

Anova Table

Response: test

Sum Sq Df F value Pr(>F)   

treat 51.511 2 4.0173 0.026616 *

severity 235.244 2 18.3466 3.21e-06 ***

treat:severity 112.356 4 4.3813 0.005468 **

Residuals      230.800 36                    

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Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

a. 18.346 b. 117.622 c. 28.089 d. 25.755

4. In terms of interpreting the interaction effect, which table of means would be of most interest?

Tables of means

Grand mean

10.84444

treat

des impl insig

   12    12     9

severity

    mild moderate   severe

      14       11        8

treat:severity

severity

treat   mild moderate severe

des 13 11 10   

impl 17 12 6   

insig 11 9 8

a. treat table. b. treat:severity table. c. severity table

5. Based on the ANOVA table presented in question 3, which of the effects in this analysis would be considered statistically significant using .01 as the alpha level? Select all that apply.

a. Main effect for severity. b. Interaction effect (treatment:severity). c. Main effect for treatment

Answer 1

1.
There are two types of treatments each with three levels (3 x 3)
Since different subjects were assigned into different treatments, this is a
c. 3x3 between subjects factorial ANOVA.

2.
The F test for the factor treatment (treat) would be described as
a. Test of main effect.

3.
MS value for the severity factor = 18.3466
a. 18.346

4.
In terms of interpreting the interaction effect, the table of means would be of most interest is
b. treat:severity table.

5.
P-value for severity and treat:severity is less than 0.01 significance level.
Thus, the effects which are statistically significant is,
a. Main effect for severity. b. Interaction effect (treatment:severity).