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Problems and Exercises I
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Independent Groups Designs

Read the following description of an experimental study carefully and then answer the questions that follow.

Description:

Executives at a large corporation hired a psychologist to evaluate two physical fitness programs that differed specifically in the degree to which diet and nutritional suggestions were part of the program. Plan N included diet/nutritional requirements for all participants. Plan E emphasized a regular exercise program for all participants, but did not require participants to change their eating habits. The nature and amount of exercise required in the two programs were essentially the same. The psychologist obtained a list of all employees who, as part of a previous survey, had indicated their desire to take part in a fitness program while at work. These people were contacted and 85% of the original group of employees were still working at the company or had not changed their minds about participating. Two hundred employees from this remaining group were randomly assigned in equal numbers (100) to either Program N or Program E. Each program lasted 6 months, during which time employee absenteeism in each group was monitored. At the end of the program, participants were given a questionnaire designed to assess attitudes toward the company and the fitness program. Because of transfers within the company, firing and quitting of employees, and other reasons not able to be documented, only 75 out of 100 employees in Group E finished the program, and only 50 of the original 100 participants from Program N completed the 6-month program. The psychologist judged that these sample sizes were still sufficiently large enough to assess adequately the effect of the program. A statistical comparison of participants from the two groups revealed that employees enrolled in Program N showed significantly less absenteeism than persons completing Program E. Moreover, the attitude assessment at the end of the program revealed that employees who completed Program N had significantly better opinions of the company and the program than did persons in Program E. On the basis of these results, the psychologist concluded that Plan N was better than Plan E.



1

What is the independent variable (and its levels) in this study?
2

What is the dependent variable? (Note: There may be more than one dependent variable associated with this experiment.)
3

Can you identify a serious threat to the internal validity of this experiment? Identify the threat and explain why it is a threat.





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