Explaining confidence The admissions director for a university found that (107.8,116.2)is a 95%confidence interval for the mean IQ score of all freshmen. Discuss whether each of the following explanations is correct, based on that information.

a. There is a 95%probability that the interval from role="math" localid="1654200953396" 107.8to116.2contains μ.

b. There is a 95%chance that the interval(107.8,116.2)contains x¯.

c. This interval was constructed using a method that produces intervals that capture the true mean in 95%of all possible samples.

d. If we take many samples, about 95%of them will contain the interval (107.8,116.2).

e. The probability that the interval (107.8,116.2)captures μ is either 0 or 1, but we don’t know which.

Short Answer

Expert verified

a. The explanation of a is incorrect.

b. The explanation of b is incorrect.

c. The explanation of c is correct.

d. The explanation of d is incorrect.

e. The explanation of e is correct.

Step by step solution

01

Given Information

95% confidence interval for mean IQ is given as(107.8,116.2)

02

To determine whether there is a 95% probability for the interval from 107.8 to 116.2 contains μ

Confidence Interval may or may not contain mean μ.

Probability will be either 0or1.

It cannot be 0.95.

Explanation is incorrect.

03

To check if there is 95% chance for the interval (107.8,116.2) contains x¯

Sample mean is generally center of given confidence interval.

Probability is 1(not0.95)

Explanation is Incorrect.

04

To check is this interval was constructed using a method that produces intervals that capture the true mean in 95% of all possible samples.

True Mean is also called Population Mean.

Here, interval of 95%of possible samples contain population/true mean.

Hence, Explanation is correct.

05

To check  if about 95% of the samples taken will contain the interval (107.8,116.2)

If sample mean is samples is same, sample contains only same confidence interval. Sample mean in a lot is identical less than 95%of possible samples.

Explanation is Incorrect.

06

To check if the probability for the interval (107.8,116.2) captures μ is either 0 or 1 but it is unknown.

Population mean may or may not contain μ.

Probability is 0or1.

Explanation is correct.

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Most popular questions from this chapter

A Gallup poll found that only 28%of American adults expect to inherit money or valuable possessions from a relative. The poll’s margin of error was ±3 percentage points at a 95%confidence level. This means that

a. the poll used a method that gets an answer within 3% of the truth about the population 95%of the time.

b. the percent of all adults who expect an inheritance must be between 25%and 31%.

c. if Gallup takes another poll on this issue, the results of the second poll will lie between 25%and 31%.

d. there’s a 95% chance that the percent of all adults who expect an inheritance is between

25% and 31%.

e. Gallup can be 95% confident that between 25% and 31% of the sample expect an inheritance.

Prayer in school Refer to Exercise 5.

a. Explain what would happen to the length of the interval if the confidence level were increased to 99%.

b. How would a 95%confidence interval based on double the sample size compare to the original 95%interval?

c. The news article goes on to say: “The theoretical errors do not take into account

additional errors resulting from the various practical difficulties in taking any survey of public opinion.” List some of the “practical difficulties” that may cause errors which are not included in the ±3 percentage point margin of error.

Explaining confidence A 95%confidence interval for the mean body mass index (BMI) of young American women is 26.8±0.6. Discuss whether each of the following explanations is correct, based on that information.

a. We are confident that 95%of all young women have BMI between 26.2and 27.4.

b. We are 95%confident that future samples of young women will have mean BMI

between 26.2and27.4.

c. Any value from 26.2to27.4is believable as the true mean BMI of young American women.

d. If we take many samples, the population mean BMI will be between 26.2and 27.4in about 95%of those samples.

e. The mean BMI of young American women cannot be 28.

A radio talk show host with a large audience is interested in the proportion p of adults in his listening area who think the drinking age should be lowered to eighteen. To find this out, he poses the following question to his listeners: “Do you think that the drinking age should be reduced to eighteen in light of the fact that 18-year-olds are eligible for military service?” He asks listeners to go to his website and vote “Yes” if they agree the drinking age should be lowered and “No” if not. Of the 100 people who voted, 70 answered “Yes.” Which of the following conditions are violated?

I. Random

II. 10%

III. Large Counts

a. I only

b. II only

c. III only

d. I and II only

e. I, II, and III

Losing weight Refer to Exercise 6.

a. Explain what would happen to the length of the interval if the confidence level was decreased to 90%.

b. How would a 95%confidence interval based on triple the sample size compare to the original 95%interval?

c. As Gallup indicates, the 3percentage point margin of error for this poll includes only sampling variability (what they call “sampling error”). What other potential sources of error (Gallup calls these “non sampling errors”) could affect the accuracy of the 95% confidence interval?

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