13.Suppose you wanted to see whether a training program helped raise students' scores on a standardized test. You administer the test to a random sample of students, give them the training program, then readminister the test. For each student, you record the increase (or decrease) in the test score from one time to the next.

1. What explanation might be given for the increased scores, other than the fact that the training program had an impact? a)The length of the training program allowed the students to become less stressed and therefore be much more relaxed on their second attempt.

b)The students didn't study for the second attempt since they had already studied for the first attempt.

c)Students generally cheat at a higher rate when taking a test a second time.

d)The students had already taken the test once, before the program, so when they took it afterward they were familiar with the test already.

2.What would have been a better way to design the study in order to rule out the explanation you gave in part (a)? a)Vary the length of the training program for different groups of students.

b)Keep everything the same but make sure each student takes the test in an isolated area to ensure that no cheating happens.

c)Randomly assign some students to take the program and others to not take it, using matched pairs if possible.

d)Randomly assign the students into two groups, controlling the amount of time each student can study for the first and second attempts.