You are assigned to direct a study on your campus to discover factors that are associated with strong academic performance. You decide to identify 20 students, who have perfect GPAs of 4.0, and then measure explanatory variables for them that you think may be important, such as high school GPA and average amount of time spent studying per day.
a. Explain what is wrong with this study design.
b. Describe a study design that would provide more useful information.