STAT 240 QUIZ 4 KEY Answers are underlined and in bold
1. Which statement about confidence intervals is FALSE?
A. A confidence interval is an interval of values computed from sample data that is likely to include
the true population value.
B. An approximate formula for a 95% confidence interval is
sample estimate  margin of error.
C. A confidence interval between 20% and 40% means that the population proportion lies
between 20% and 40%.
D. A 99% confidence interval procedure has a higher probability of producing intervals that will
include the population parameter than a 95% confidence interval procedure.
2. The multiplier for a confidence interval is determined by:
A. The desired level of confidence and the sample size
B. The desired level of confidence but not the sample size
C. The sample size but not the desired level of confidence
D. Neither the sample size nor the level of confidence
3. A randomly selected sample of 400 students at a university with 15-week semesters was asked whether
or not they think the semester should be shortened to 14 weeks (with longer classes). This information
will be used to estimate the percent of all students at the university favoring the shorter semester. Fortysix percent (46%) of the 400 students surveyed answered "yes." The number 46% is a ___
A. population parameter. B. sample statistic C. margin of error D. standard error.
4. In a poll of n = 200 randomly selected individuals, 60 people said they are opposed to the death
penalty for persons convicted of murder. Which choice correctly shows the calculation of the margin of
error for a 95% confidence interval for the population proportion opposed to the death penalty?
0.3(1  0.3)
0.3(1  0.3)
0.6(1  0.6)
1
A.
B 2
C. 2 
D. 2 
200
60
200
60
5. Which of these statements best describes the purpose of a confidence interval for a proportion?
A. It estimates the proportion of a sample that has a particular trait or opinion.
B. It estimates the proportion of a population that has a particular trait or opinion.
6. Suppose that 200 different polling organizations and academic researchers all do surveys in which the
same question is asked. All 200 research groups construct a 90% confidence interval for the proportion
who would say "yes" to this question. About how many of the 200 different 90% confidence intervals will
capture the true population proportion?
A. 10
B. 90
C. 180
D. 200
7. For a survey of American diets a random sample of 1000 people were contacted. Of the 1000 people,
340 people completed the questionnaire. The results of this study, if applied to all Americans, are
questionable because of
A. large margin of error B. Selection bias C. Nonresponse bias
D. Response bias
8. For the same data set, how will the width of a 95% confidence interval for a percent compare to the
width of a 98% confidence interval?
A. The 95% confidence interval will be wider than the 98% interval
B. The 98% confidence interval will be wider than the 95% confidence interval
C. It depends - sometimes the 95% interval will be wider, sometimes the 98% interval will be wider
9. A national polling organization does a survey of 995 people to estimate the percentage of all
American adults who favor a ban on the use of cell phones while driving. In the survey, 37% said they
favor such a ban. The sample was selected using random digit dialing. Which of the following is the
sampleing frame for this survey?
A. The 995 individuals surveyed.
B. The 37% who favor banning the use of cell phomes while driving
C. All American adults
D. All American adults with a telephomne in their household.
10. Which of the following sampling methods is most likely to produce bias in the sample results?
A. A simple random sample with n = 500
B. A stratified sample with n=500
C. A volunteer sample with n=500
D. A simple random sample with n = 200
11. Which of the following is a benefit of increasing the sample size of a survey?
A. A larger sample size decreases the response bias
B. A large sample size decreases the margin of error
C. A large sample size insures that the sampling frame represents the population.
12. The Gallup Poll divides the country into four regions and then samples 250 individuals from each
region. What type of sampling method is this?
A. Simple random
B. Systematic
C. Biased
D. Stratified
13. Taxpayers in a population are listed in order of increasing income, with people with the lowest
incomes listed first. A sample is selected by randomly choosing one of the first 100 names, then choosing
every 100th name from that point forward. This is an example of a ______ sample.
A. stratified
B cluster
C. simple random
D. systematic
-------------------------------------------------------------------------------------------------------------14. Which of the following random samples will provide the smallest margin of error? Assume all other
factors are equal other than the given information.
A. sample n = 400 from a population of 10 million
B. sample n =1,500 from a population of 100 million
C. sample n = 600 from a population of 30 million
15. The following Minitab output gives 95% confidence intervals for the proportions of females and
males opposed to stronger gun permit laws in the U.S. The data are from a national survey done by the
University of Chicago.
Variable
gunlaw_Female
gunlaw_Male
X
66
119
n
599
456
Sample p
0.110
0.261
95.0% CI
(0.085, 0.135)
(0.221, 0.301)
Which statement is true?
A. It’s reasonable to say that U.S. females and males do not differ with regard to the gun permit issue
B. We can reject the statement that 10% of U.S. females are opposed to stronger gun permit laws
C. We can reject the statement that 15% of U.S. males are opposed to stronger gun permit laws
D. For females, the proportion 0.110 is an example of a population parameter