2.1 Section Title
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Critical Thinking Exercise
Exercise and Mood
Nadine, who teaches aerobics at a local health club, believes that regular aerobic exercise improves people’s mood and overall sense of well-being. She tells one of her classes of longtime aerobics enthusiasts about her hunch, and many of them respond eagerly to her request for volunteers to participate in a one-month test of her hypothesis. Ten volunteers from the class are assigned to the experimental group and are instructed to complete a mood questionnaire after their aerobics class each week. To make up a control group, Nadine talks to a group of people waiting to see a movie at the theater next to the health club. After describing the purpose of her study, Nadine asks for volunteers, promising them five free movie passes for their participation. She then arranges for the 10 control participants to return to the theater one day each week for the next month, during which time they will watch a documentary film that lasts exactly the same amount of time as the aerobics class. After each film, the control group completes the same mood questionnaire. After checking the questionnaires at the end of the one-month period, Nadine is delighted to find that the average mood rating of the participants in the exercise group is substantially higher than that of the participants in the control group.
Question
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This is an example of a quasi-experimental study because the comparison groups (exercisers and moviegoers) differ on the variable of interest at the outset of the study. The data are collected in the field (at the aerobics class or the theater) using questionnaires.
Question
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The hypothesis is that engaging in regular aerobic exercise improves people’s mood and overall sense of well-being.
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The independent variable is the type of activity the volunteers engage in (one month of participation in a weekly aerobic exercise class or watching, once a week, a documentary film that lasts exactly the same amount of time as the aerobics class).
Question
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The dependent variable is each participant’s weekly responses on a mood questionnaire.
Question
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Three variables that are controlled are:
a. Type of activity (exercise versus movie viewing) during the weekly aerobics classes.
b. Duration of activity (moviegoers watch a film that lasts exactly as long as the aerobics class).
c. Measurement of responses to the mood questionnaire over the same time period (one month).
Question
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Several variables are uncontrolled:
a. The absence of random assignment leaves open alternative explanations for mood elevation in the exercise group. As volunteers and long-time fitness enthusiasts, participants in the aerobics class may have been more highly motivated than a group of randomly selected adults would be. In addition, people who exercise are less likely to be depressed than their counterparts who do not. Therefore, differences in mood between the exercise and control groups could reflect pre-existing differences rather than differences due to the manipulation of the IV (type of activity).
b. Knowledge of the researcher’s hypothesis (by both exercisers and moviegoers) may have influenced the results such that the experimental group outscored the control group on the mood questionnaire.
c. Other daily activities, such as additional exercise, dieting, or relaxation, might have differentially influenced the mood of the two groups.
d. Since the researcher was interested in aerobic exercise, a more appropriate activity for the control group than watching a film would have been some form of nonaerobic exercise—weight training, for example.
Question
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No. Since so many variables were not controlled, virtually nothing can be concluded from this study. A more valid test would involve participants with similar exercise backgrounds who were not informed of the researcher’s hypothesis, and who had been pretested and matched for comparable fitness levels before being randomly assigned to the control and experimental groups.