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Chapter 10: Q.74 (page 660)

Coaching and SAT scores: Critique (4.1,4.3) The data you used in the previous two exercises came from a random sample of students who took the SAT twice. The response rate was 63%, which is pretty good for nongovernment surveys.

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

(b) We can鈥檛 be sure that coaching actually caused the coached students to gain more than the un-coached students. Explain briefly but clearly why this is so

Short Answer

Expert verified

a). The results cannot be generalized to the entire population.

b). An observational study cannot prove causation, only an experiment is capable of proving causation.

Step by step solution

01

Part (a) Step 1: Given Information

The response rate was 63%, which is pretty good for nongovernment surveys.

02

Part (a) Step 2: Explanation

The people who responded might have a very different result than those who did not respond. For example, people with very low scores will most likely be to embarrassed to respond.

Since the scores of the nonresponses could be very different from the scores of the responders, the true values and conclusions might be very different for the two groups.

Thus the results cannot be generalized to the entire population.

03

Part (b) Step 1: Given Information

The response rate was 63%, which is pretty good for nongovernment surveys.

04

Part (b) Step 2: Explanation

Individuals are purposely subjected to a treatment in order to examine their reactions in an experiment.

An observational study tries to gather information without disturbing the scene they are observing.

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Most popular questions from this chapter

A study of road rage asked separate random samples of 596men and 523women about their behavior while driving. Based on their answers, each re-spondent was assigned a road rage score on a scale of 0to 20. Are the conditions for performing a two-sample t test satisfied?

a) Maybe; we have independent random samples, but we need to look at the data to check Normality.

(b) No; road rage scores in a range between 0 and 20 can鈥檛 be Normal.

(c) No; we don鈥檛 know the population standard deviations.

(d) Yes; the large sample sizes guarantee that the corresponding population distributions will be Normal.

(e) Yes; we have two independent random samples and large sample sizes.

A sample survey interviews SRSs of500female college students and 550male college students. Each student is asked whether he or she worked for pay last summer. In all, 410of the women and 484of the men say 鈥淵es.鈥� The 95%confidence interval for the difference pM-pFin the proportions of college men and women who worked last summer is about

(a) 0.06卤0.00095

(b) 0.06卤0.043.

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46. Happy customers As the Hispanic population in the United States has grown, businesses have tried to understand what Hispanics like. One study inter-viewed a random sample of customers leaving a bank. Customers were classified as Hispanic if they preferred to be interviewed in Spanish or as Anglo if they preferred English. Each customer rated the importance
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Do drivers reduce excessive speed when they encounter police radar? Researchers studied the behavior of a sample of drivers on a rural interstate highway in Maryland where the speed limit was 55miles per hour. They measured the speed with an electronic device hidden in the pavement and, to eliminate large trucks, considered only vehicles less than 20feet long. During some time periods (determined at random), police radar was set up at the measurement location. Here are some of the data.

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Coaching and SAT scores (10.2) What we really want to know is whether coached students improve more than uncoached students and whether any advantage is large enough to be worth paying for. Use the information above to answer these questions:

(a) Is there good evidence that coached students gained more on average than uncoached students? Carry out a significance test to answer this question.

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