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Experiments with Two Groups

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Understanding Experiments with Two Groups

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.


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 10-1
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 10-1. The statistical analysis is a(n) __________ sample t test.
a. independent
b. correlated
c. paired
d. repeated measures

2. Consult Table 10-1. How many participants were in the study?
a. 15
b. 28
c. 30
d. None of the above.

3. Consult Table 10-1. 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 10-1. 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 10-1. 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 10-1. 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

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1. I do not understand the worksheet for this project. Please explain. I have attached this to the file.

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This solution provides assistance with the questions in the the two worksheets, including highlighting the information in the tables for easy understanding and referencing.