Seat belt uses 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.16 Explain the reason for the bias observed in responses to the survey. Do you expect bias in the same direction in most surveys about seat belt use?

Short Answer

Expert verified

It is not expected that all the surveys about the seat belt will be in the same direction.

Step by step solution

01

Given information

The use of seat belts by drivers was investigated in an EL Paso, Texas study. Drivers were monitored at convenience stores picked at random. They were asked to answer questions after getting out of their cars, including questions about seat belt use. Although75% of respondents indicated they always wear seat belts, only 61.5 percent were doing so when they pulled into the store parking lots.

02

Concept

A simple random sample (SRS) of size n is made up of n people chosen from the population with an equal chance of being the sample that is actually chosen.

03

Explanation

A selection bias or a non-response bias could occur. Most persons who do not wear seat belts are unlikely to tell you the truth. As a result, the results will be skewed, and the sample will not be representative of the full population. As a result, it is unlikely that all seat belt polls will point in the same way.

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Most popular questions from this chapter

An example of a non-sampling error that can reduce the accuracy of a sample survey is

(a) using voluntary response to choose the sample.

(b) using the telephone directory as the sampling frame.

(c) interviewing people at shopping malls to obtain a sample.

(d) variation due to chance in choosing a sample at random.

(e) inability to contact many members of the sample.

Acupuncture and pregnancy A study sought to determine whether the ancient Chinese art of acupuncture could help infertile women become pregnant.41 One hundred sixty healthy women undergoing treatment with artificial insemination were recruited for the study. Half of the subjects were randomly assigned to receive acupuncture treatment 25minutes before embryo transfer and again 25

minutes after the transfer. The remaining 80subjects were instructed to lie still for 25minutes after the embryo transfer.

Results: In the acupuncture group, 34women became pregnant. In the control group, 21women became pregnant.

(a) Describe how the three principles of experimental design were addressed in this study.

(b) The difference in the percent of women who became pregnant in the two groups is statistically significant. Explain what this means to someone who

knows little statistics.

(c) Explain why the placebo effect prevents us from concluding that acupuncture caused the difference in pregnancy rates.

Look, Ma, no hands! Does talking on a hands-free cell phone distract drivers? Researchers recruit 40student subjects for an experiment to investigate this question. They have a driving simulator equipped with a hands-free phone for use in the study.

(a) Researchers are considering the design shown in the figure below. What type of design is this?

(b) Explain how blocking could be used to improve the design in (a).

(c) Why is it important to randomly assign the treatments within each block?

Archaeologists plan to examine a sample of 2-meter square plots near an ancient Greek city for artifacts visible in the ground. They choose separate random samples of plots from the floodplain, coast, foothills, and high hills. What kind of sample is this?

(a) A cluster sample

(b) A convenience sample

(c) A simple random sample

(d) A stratified random sample

(e) A voluntary response sample

Describe how you would carry out the random assignment. Provide enough detail that a classmate could implement your procedure.

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