18. Explaining confidence The admissions director from Big City University found that (107.8, 116.2) is a 95% confidence interval for the mean IQ score of all freshmen. Comment on whether or not each of the following explanations is correct.
(a) There is a 95%probability that the interval from 107.8to 116.2contains 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) 95%of all possible samples will contain the interval (107.8,116.2).

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

Short Answer

Expert verified

(a) The explanation that there is a 95% probability that the interval from
107.8to 116.2contains μis incorrect.

(b) The explanation that there is a 95%chance that the interval (107.8,116.2)contains xis incorrect.

(c) The explanation that the interval was constructed using a method that
produces intervals that capture the true mean in 95%of all possible samples is correct.

(d) The explanation that 95% of all possible samples will contain the inter-
val (107.8,116.2) is incorrect.

(e) The explanation that the probability that the interval (107.8,116.2)captures μis either 0or 1is correct.

Step by step solution

01

Part (a) Step 1: Given information

To determine that there is a 95%probability that the interval from 107.8to 116.2 contains μ is correct or not.

02

Part (a) Step 2: Explanation

Let, the confidence interval is 95%.
And the mean IQis 107.8to116.2.
In the range of 107.8to 116.2, the 95 percent probability does not contain the true population mean μ of all samples.
As a result, the explanation is incorrect.

03

Part (b) Step 1: Given information

To determine that there is a 95%chance that the interval (107.8,116.2)contains xis correct or not.

04

Part (b) Step 2: Explanation

Let, the confidence interval is 95%.
And the mean IQis 107.8to 116.2.
The probability of finding the sample mean x is 95percent. However, the sample mean x is identical to the confidence interval's center.
Hence, the probability is 1.
As a result, the explanation is incorrect.

05

Part (c) Step 1: Given information

To determine that the interval was constructed using a method that
produces intervals that capture the true mean in 95% of all possible samples is correct or not.

06

Part (c) Step 2: Explanation

Let, the confidence interval is 95%.
And the mean IQis 107.8to 116.2.
The true mean of all possible samples is included within the 95 percent confidence interval between 107.8 and 116.2.
As a result, the explanation is correct.

07

Part (d) Step 1: Given information

To determine that the 95%of all possible samples will contain the interval (107.8,116.2)is correct or not.

08

Part (d) Step 2: Explanation

Let, the confidence interval is 95%.
And the meanIQis 107.8to 116.2.
The interval between 107.8and 116.2does not contain real population mean μin the 95 percent probability.
As a result, the samples have a confidence interval of less than 95 percent for all potential samples.
As a result, the explanation is incorrect.

09

Part (e) Step 1: Given information

To determine that the probability that the interval (107.8,116.2)captures μis either 0or 1, is correct or not.

10

Part (e) Step 2: Explanation

Let, the confidence interval is 95%.
And the mean IQis 107.8to 116.2.
The confidence interval from 107.8to 116.2 does not contain the true population mean μ for all samples.

Hence, the probability is either 1or 1.
As a a result, the explanation is correct.

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Most popular questions from this chapter

Hallux abducto valgus (call it HAV) is a deformation of the big toe that is fairly uncommon in youth and often requires surgery. Doctors used X-rays to measure the angle (in degrees) of deformity in a random sample of patients under the age of 21who came to a medical center for surgery to correct HAV. The angle is a measure of the seriousness of the deformity. For these 21patients, the mean HAV angle was 24.76degrees and the standard deviation was 6.34degrees. A dot plot of the data revealed no outliers or strong skewness.

(a) Construct and interpret a 90%confidence interval for the mean HAV angle in the population of all such patients.

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These results are based on telephone interviews with a randomly selected national sample of 1028teenagers in the Gallup Poll Panel of households, aged 13to 17. For results based on this sample, one can say . . . that the maximum error attributable to sampling and other random effects is ±3percentage points. In addition to sampling error, question-wording and practical difficulties in conducting surveys can introduce error or bias into the findings of public opinion polls.16

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