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Chapter 4: Q. 30 (page 239)

Seat belt use A study in El Paso, Texas, looked at seat belt use by drivers. Drivers were

observed at randomly chosen convenience stores. After they left their cars, they were

invited to answer questions that included questions about seat belt use. In all, 75% said

they always used seat belts, yet only 61.5% were wearing seat belts when they pulled into

the store parking lots. Explain why the two percentages are so different.

Short Answer

Expert verified

The two percentages are so different because of the biasing as bias makes the sample results not representative for the real situation.

Step by step solution

01

Given information

We need to explain that why the two percentages are so different.

02

Explanation

Selection or undercoverage bias excludes a portion of the population, measurement or response bias employs a method that yields numbers that differ from the real value, and nonresponse bias arises from the lack of data for everyone in the sample.

Most individuals will refuse to confess that they do not use a seat belt since they are aware that they should.

As a result, untruthful responses may be given, and measurement bias may be present in the sample. Bias causes sample results to be unrepresentative of the real world.

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Most popular questions from this chapter

Doctors and nurses Nurse-practitioners are nurses with advanced qualifications who often act much like primary-care physicians. Are they as effective as doctors at treating patients with chronic conditions? An experiment was conducted with 1316patients who had been diagnosed with asthma, diabetes, or high blood pressure. Within each condition, patients were randomly assigned to either a doctor or a nurse-practitioner. The response variables included measures of the patients' health and of their satisfaction with their medical care after 6months.50

a. Which are the blocks in this experiment: the different diagnoses (asthma, diabetes, or high blood pressure) or the type of care (nurse or doctor)? Why?

b. Explain why a randomized block design is preferable to a completely randomized design in this context.

c. Suppose the experiment used only diabetes patients, but there were still 1316subjects willing to participate. What advantage would this offer? What disadvantage?

iPhonesSuppose 1000iPhones are produced at a factory today. Management would like to ensure that the phones’ display screens meet their quality standards before shipping them to retail stores. Because it takes about 10minutes to inspect an individual phone’s display screen, managers decide to inspect a sample of 20phones from the day’s production.

a. Explain why it would be difficult for managers to inspect an SRS of 20iPhones that are produced today.

b. An eager employee suggests that it would be easy to inspect the last 20iPhones that were produced today. Why isn’t this a good idea?

c. Another employee recommends a different sampling method: Randomly choose one of the first50 iPhones produced. Inspect that phone and every fiftieth iPhone produced afterward. (This method is known as systematic random sampling.) Explain carefully why this sampling method is not an SRS.

Oils and inflammation The extracts of avocado and soybean oils have been shown to slow cell inflammation in test tubes. Will taking avocado and soybean unsaponifiables (called ASU) help relieve pain for subjects with joint stiffness due to arthritis? In an experiment, 345 men and women were randomly assigned to receive either

300 milligrams of ASU daily for three years or a placebo daily for three years.

Explain why it was necessary to include a control group in this experiment.

Corn variety 1yielded 140bushels per acre last year at a research farm. This year, corn

variety 2, planted in the same location, yielded only 110bushels per acre. Based on these

results, is it reasonable to conclude that corn variety 1is more productive than corn variety

2?

a. Yes, because 140bushels per acre is greater than 110bushels per acre.

b. Yes, because the study was done at a research farm.

c. No, because there may be other differences between the two years besides the corn

variety.

d. No, because there was no use of a placebo in the experiment.

e. No, because the experiment wasn’t double-blind.

Improving response rate -How can we reduce the rate of refusals in telephone surveys? Most people who answer at all listen to the interviewer’s introductory remarks and then decide whether to continue. One study made telephone calls to randomly selected households to ask opinions about the next election. In some calls, the interviewer gave her name; in others, she identified the university she was representing; and in still others, she identified both herself and the university. For each type of call, the interviewer either did or did not offer to send a copy of the final survey results to the person interviewed.

a. List the factors in this experiment and state how many levels each factor has.

b. If the researchers used every possible combination to form the treatments, how many treatments were included in the experiment?

c. List two of the treatments.
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