Part D
In a large study designed to compare the risk of cardiovascular disease (CVD) between smokers
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and nonsmokers, random samples from each group were selected. The sample proportion of pe
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ople with CVD was calculated for each group, and a 95 percent confidence interval for the differ
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ence (smoker minus nonsmoker) was given as (−0.01, 0.04). Which of the following is the best in
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terpretation of the interval? - O O O O
OANSWER B. We are 95% confident that the difference in proportions for smokers and nonsmoke
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rs with CVD in the population is between −0.01 and 0.04.
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A research group studying cell phone habits asked the question "Do you ever use your cell phon
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e to make a payment at a convenience store?" to people selected from two random samples of c
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ell phone users. One sample consisted of older adults, ages 35 years and older, and the other sa
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mple consisted of younger adults, ages 18 years to 34 years. The proportion of people who answ
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ered yes in each sample was used to create a 95 percent confidence interval of (0.097, 0.125) to
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estimate the difference (younger minus older) between the population proportions of people w
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ho would answer yes to the question. Which of the following is the best description of what is m
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eant by 95 percent confidence? -
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OANSWER C. In repeated random sampling with the same sample size, approximately 95% of the
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intervals constructed from the samples will capture the difference in population proportions of
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people who would answer yes to the question.
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Consider a 90 percent confidence interval constructed to estimate the difference between two p
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opulation proportions. Which of the following is the best interpretation of what is meant by 90
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percent confidence? - O O
ANSWER D. For repeated random sampling from the populations with samples of the same size,
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approximately 90% of the confidence intervals constructed will capture the true difference bet
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ween the population proportions.
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Surveys were sent to a random sample of owners of all-wheel-
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drive (AWD) vehicles and to a random sample of owners of front-wheel-
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drive (FWD) vehicles. The proportion of owners who were satisfied with their vehicles was recor
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ded for each sample. The sample proportions were used to construct the 95 percent confidence
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, interval for a difference in population proportions (FWD minus AWD) for satisfied owners. The in
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terval is given as (−0.01, 0.12).
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A car company believes that the proportion of satisfied owners of AWD vehicles differs from the
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proportion of satisfied owners of FWD vehicles. Does the confidence interval provide evidence t
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hat this belief is plausible? - ANSWER A. No. The interval contains 0.
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A large company offered gym memberships to its employees as part of a program to keep emplo
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yees healthy. A random sample of employees with a gym membership and a random sample of
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employees without a gym membership were taken, and the proportion of employees who had t
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aken at least one sick day in the past month was recorded for each sample. A 90 percent confide
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nce interval for the difference in population proportions (membership minus no membership) w
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as found to be (−0.13, 0.05).
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Employees believe that there is no difference in absenteeism between those with a gym membe
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rship and those without a gym membership. Does the confidence interval provide evidence that
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this belief is plausible? -
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OANSWER E. Yes. The value of 0 is contained in the interval, which indicates that no difference is
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plausible.
A 90 percent confidence interval for the proportion difference p1 − p2 was calculated to be (0.24
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7, 0.325).
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Which of the following conclusions is supported by the interval? -
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OANSWER C. There is evidence to conclude that p1 > p2 because all values in the interval are posi
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tive.
A yearbook company was investigating whether there is a significant difference between two sta
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tes in the percents of high school students who order yearbooks. From a random sample of 150
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students selected from one state, 70 had ordered a yearbook. From a random sample of 100 stu
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dents selected from the other state, 65 had ordered a yearbook. Which of the following is the m
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