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Confidence Interval Estimation
CHAPTER 8: CONFIDENCE INTERVAL ESTIMATION
1.
The width of a confidence interval estimate for a proportion will be
a)
narrower for 99% confidence than for 95% confidence.
b)
wider for a sample size of 100 than for a sample size of 50.
c)
narrower for 90% confidence than for 95% confidence.
d)
narrower when the sample proportion is 0.50 than when the sample proportion is 0.20.
ANSWER:
c
TYPE: MC
DIFFICULTY: Moderate
KEYWORDS: confidence interval, proportion, properties, width
2.
When determining the sample size for a proportion for a given level of confidence and sampling
error, the closer to 0.50 that
p
is estimated to be, the sample size required __________.
a)
is smaller
b)
is larger
c)
is not affected
d)
can be smaller, larger or unaffected
ANSWER:
b
TYPE: MC
DIFFICULTY: Moderate
KEYWORDS: confidence interval, proportion, properties
3.
A 99% confidence interval estimate can be interpreted to mean that
a)
if all possible samples are taken and confidence interval estimates are developed, 99% of
them would include the true population mean somewhere within their interval.
b)
we have 99% confidence that we have selected a sample whose interval does include the
population mean.
c)
Both of the above.
d)
None of the above.
ANSWER:
c
TYPE: MC
DIFFICULTY: Moderate
KEYWORDS: confidence interval, interpretation
4.
If you were constructing a 99% confidence interval of the population mean based on a sample of
n
=25 where the standard deviation of the sample
s
= 0.05, the critical value of
t
will be
a)
2.7969
b)
2.7874
c)
2.4922
d)
2.4851
ANSWER:
a
TYPE: MC
DIFFICULTY: Easy
KEYWORDS: critical value,
t
distribution
5.
Which of the following is
not
true about the Student’s
t
distribution?
a)
It has more area in the tails and less in the center than does the normal distribution.
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Confidence Interval Estimation
b)
It is used to construct confidence intervals for the population mean when the population
standard deviation is known.
c)
It is bell shaped and symmetrical.
d)
As the number of degrees of freedom increases, the
t
distribution approaches the normal
distribution.
ANSWER:
b
TYPE: MC
DIFFICULTY: Easy
KEYWORDS:
t
distribution, properties
6.
True or False:
The
t
distribution is used to construct confidence intervals for the population
mean when the population standard deviation is unknown.
ANSWER:
True
TYPE: TF
DIFFICULTY: Easy
KEYWORDS: confidence interval, mean, standard deviation unknown
7.
The
t
distribution
a)
assumes the population is normally distributed.
b)
approaches the normal distribution as the sample size increases.
c)
has more area in the tails than does the normal distribution.
d)
All of the above.
ANSWER:
d
TYPE: MC
DIFFICULTY: Easy
KEYWORDS:
t
distribution, properties
8.
It is desired to estimate the average total compensation of CEOs in the Service industry. Data
were randomly collected from 18 CEOs and the 97% confidence interval was calculated to be
($2,181,260, $5,836,180). Which of the following interpretations is correct?
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 Fall '07
 Reich

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