Chapter 8.1, Problem 21E

(a)

To determine

To Explain: the confidence interval.

Answer to Problem 21E

It is expected about 90% of all possible samples to have a 90% confidence interval that have the correct average travel times to work for all employed California adults.

Explanation of Solution

The 90% confidence interval shows the average travel times to work for all employed California adults.90% confidence implies that it is predicted about 90% of all samples to have 90% confidence interval that has the correct population parameter.

In this case, it is predicted about 90% of all possible samples to have a 90% confidence interval that have the correct average travel times to work for all employed California adults.

(b)

To determine

To find: the drawbacks do these actions have.

Explanation of Solution

It can reduce the margin of error by:

• Increasing the sample size, the reason is that a large sample size would result in more detail about the population and therefore the estimates are more accurate. A drawback is that it is more time consuming and costly to collect data for a larger sample.
• Decreasing the confidence level. The reason is that there are less confident that the confidence interval has the correct population parameter and therefore the confidence interval then have less possible values for the correct population parameter. A drawback is that there are less confident that the confidence interval would have the correct population parameter.

(c)

To determine

To Explain: the non response may lead to bias in this survey and the statement margin of error account for this possible data.

Explanation of Solution

Non response bias is the results of not contain data for everybody in the sample.

It is possible that the people for whom do not have any data have exact common characteristics, which leads to consistently overestimate or consistently underestimate the true population parameters, then this would cause bias in our sample.

The margin of error only accounts for the possible variation and therefore is not include non response bias.