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    Experiments with Two Groups

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    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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