Coaching and SAT scores: Critique (4.1, 4.3) The data in Exercises 55 and 56 came from a random sample of students who took the SAT twice. The response rate was 63%, which is fairly good for nongovernment surveys.

(a) Explain how nonresponse could lead to bias in this study.

(b) We can’t be sure that coaching actually caused the coached students to gain more than the uncoached students. Explain briefly but clearly why this is so.