Assignment:
Understanding Experiments with Two Groups
1 Twenty sets of depressed twins are obtained for a study on the effects of a new antidepressant. In each twin set, one twin is assigned to receive the drug, and the other is designed to receive the placebo. Three months later, depression levels are measured on a scale from 1 (not at all depressed) to 7 (very depressed). The following data was obtained:
Group 1 = Received drug
Group 2 = Received placebo
Variable = Depression level
Group N Mean SD
Group 1 10 3.21 1.035
Group 2 10 5.77 1.772
t = 5.785 df = 9 p = 0.017 Cohen's d = .88
1. What is the independent variable?
2. What is the dependent variable?
3. What is the scale of measurement for the dependent variable?
4. What kind of research design was used?
5. What kind of statistical analysis was used?
6. Write an APA-format conclusion.
2. The following questions refer to the following computer output in which a researcher compared the GPA of traditional (aged 18-22) and nontraditional (aged 23 or older) students.
Table 1
Group 1 = Aged 18-22
Group 2 = Aged 23 or older
Variable = Grade point average
Group N Mean SD Standard Error
Group 1 15 2.95 0.556 0.143
Group 2 15 3.08 0.524 0.135
Fmax test F = 0.225 p = 0.639
Equal Variances Assumed
t = -0.68 df = 28 p = 0.509
Equal Variances Not Assumed
t = -0.68 df = 27.90 p = 0.509
1. Consult Table 1. The statistical analysis is a(n) __________ sample t test.
a. independent
b. correlated
c. paired
d. repeated measures
2. Consult Table 1. How many participants were in the study?
a. 15
b. 28
c. 30
d. None of the above.
3. Consult Table 1. The mean GPA for traditionally-aged students was ______ and the mean GPA for nontraditionally-aged students was _______.
a. 3.08; 2.95
b. 0.556; 0.524
c. 2.95; 3.08
d. 0.524; 0.556
4. Consult Table 1. The data indicate ________ of variance; therefore, we should use the output under _________________.
a. homogeneity; "Equal Variances Assumed"
b. homogeneity; "Equal Variances Not Assumed"
c. heterogeneity; "Equal Variances Assumed"
d. heterogeneity; "Equal Variances Not Assumed"
5. Consult Table 1. The p-value is _______ than .05; therefore, we should conclude that there _______ a difference between the groups.
a. less; is
b. less; is not
c. greater; is
d. greater; is not
6. Consult Table 1. The difference in means ______ significant; therefore, we conclude that the difference between the two means is due to ________.
a. is; the independent variable
b. is; chance
c. is not; the independent variable
d. is not; chance
3. In the following study, participants were randomly assigned to receive humanistic therapy, psychodynamic therapy, or behavioral therapy for their depression. Six months after therapy ended, participants' levels of depression were rated on a Likert scale from 1 (not at all depressed) to 15 (extremely depressed).
1. Is this a two-group design or a multiple-group design? How do you know?
2. This study is an independent groups design. How do you know?
3. How could you change this experiment to be a repeated measures design?
4. How could you change this experiment to be a matched sets design?
5. Is this a true experiment or an ex post facto study? How do you know?
6. What is the independent variable in this study?
7. What is the dependent variable in this study?
8. What is the scale of measurement for the dependent variable?
9. What kind of statistical analysis was conducted?