Scenario #2: A researcher is interested in how the amount of sleep a person gets and her/his dietary intake affects cognitive functioning. He devises a study in which he selects 240 participants from a target population of 30-year-olds. He randomly assigns 80 subjects to a group who will sleep their normal amount of sleep each day for 30 days. He also randomly assigns 80 subjects to a group who will sleep one more hour than their normal amount of sleep for 30 days, and he randomly assigns 80 participants to a group who will sleep one less hour than their normal amount of sleep for 30 days. During the first 10 days, each participant group consumes 25% less than the recommended daily allowance of calories for their age and sex. During the next 10 days, each participant group consumes the recommended daily allowance of calories for their age and sex. During the final 10 days of the study, each group consumes 25% more than the recommended daily allowance of calories for their age and sex. The researcher administers a distinct but comparable intelligence test on the 10th day, 20th day, and 30th day of the study.
- Is this study an example of an independent groups design, a correlated groups design, or a mixed assignment design? Provide a rationale for your answer.
- Is this design the best one to answer the researcher’s questions? Why or why not? What changes, if any, would you recommend to improve the quality of this study?
- How many factors and levels are there in this study, and what are the names of the factors and levels?
- Provide an example of a main effect, a simple main effect, and an interaction based on the current design of this study.
- Assume that the researcher observes significant F statistics for all main effects but does not observe any simple main effects or interaction effects for this study. How should the researcher proceed to isolate the causes of these effects and begin to draw causal inferences about the findings?