Suppose a graduate student does a survey of undergraduate study habits on her university campus. She collects data on students who are in different years in college by asking them how many hours of course work they do for each class in a typical week. A sample of four students provides the following data on year in college and hours of course work per class: Student Year in College Course Work Hours per Class 1 Freshman (1) 7 2 Sophomore (2) 6 3 Junior (3) 4 4 Senior (4) 1