A high school administrator wants to determine whether positive reinforcement improves student performance. A group of students is randomly selected from the high school population. Their last year's records are examined for their GPAs. Beginning the first day of the school year and continuing through the first semester, the selected students receive a reward (free movie tickets) whenever they pass a major test. At the end of the first semester, their GPAs for the semester are calculated and compared to the last year's GPAs.
(a) Comment on this design. Identify biases, concerns, and why you might question any results.
(b) Suggest an improved design. Be sure to specify your design completely; include a diagram if appropriate; discuss how you would implement your study.