Exam 8: Confidence Interval Estimation

(A)Construct a 99% confidence interval for the standard deviation of the number of hours this firm's employees spend on work-related activities in a typical week. (B)Interpret the 99% confidence interval constructed in (A). (C)Given the target range of 40 to 60 hours of work per week,should senior management be concerned about the number of hours their employees are currently devoting to work? Explain why or why not.

The approximate standard error of the point estimate of the population total is .

When you calculate the sample size for a proportion,you use an estimate for the population proportion; namely .A conservative value for n can be obtained by using = _____.

The approximate standard error of the point estimate of the population total is:

(A)Determine a 95% confidence interval for the proportion defective for the process today. (B)Based on your answer to (A),is it still reasonable to think the overall proportion defective produced by today's process is actually the targeted 4%? Explain your reasoning. (C)The confidence interval in (A)is based on the assumption of a large sample size.Is this sample size sufficiently large in this example? Explain how you arrived at your answer. (D)How many units would have to be sampled to be 95% confident that you can estimate the fraction of defective parts within 2% (using the information from today's sample)?

(A)Construct a 95% confidence interval estimate of the population proportion of all customers who still own the cars they purchased six years ago (B)How can the result in (A)be used by the automobile dealer to study satisfaction with cars purchased at the dealership?

(A)Compute a 95% confidence interval for the true proportion of people who favor Coke.Do the results of this poll convince you that a majority of people favors Coke? (B)Suppose 2,000 (not 400)people were polled and 53% favored Coke.Would you now be convinced that a majority of people favor Coke? Why might your answer be different than in (A)? (C)How many people would have to be surveyed to be 95% confident that you can estimate the fraction of people who favor Coca-Cola within 1%?

The chi-square and F-distributions are used primarily to make inferences about population ___________.

You are told that a random sample of 150 people from Iowa has been given cholesterol tests,and 60 of these people had levels over the "safe" count of 200.Construct a 95% confidence interval for the population proportion of people in Iowa with cholesterol levels over 200.

(A)Construct a 95% confidence interval for the mean playing time of all Willie Nelson recordings. (B)Interpret the confidence interval you constructed in (A).

(A)Construct a 95% confidence interval for the difference between the proportions of online and classroom customers who pass the final exam. (B)Interpret the confidence interval obtained in (A).

When samples of size n are drawn from a population,then the sampling distribution of the sample mean is approximately normal,provided that n is reasonably large.

(A)Use the sample data to generate a 95% confidence interval for the mean difference between the appraised values and selling prices of the houses sold in Grand Rapids. (B)Interpret the constructed confidence interval fin (A)for the real estate agent.

When we replace with the sample standard deviation (s),we introduce a new source of variability and the sampling distribution becomes the _____.

The number of degrees of freedom needed to construct 90% confidence interval for the difference between means when the data are gathered from paired samples,with 15 observations in each sample,is:

If we cannot make the strong assumption that the variances of two samples are equal,then we must use the pooled standard deviation in calculating the standard error of a difference between the means.

If a sample has 20 observations and a 95% confidence estimate for is needed,the appropriate value of t-multiple is 2.093

If you are constructing a confidence interval for a single mean,the confidence interval will _____ with an increase in the sample size.

You are trying to estimate the average amount a family spends on food during a year.In the past,the standard deviation of the amount a family has spent on food during a year has been approximately $1200.If you want to be 99% sure that you have estimated average family food expenditures within $60,how many families do you need to survey?

If you increase the confidence level,the confidence interval _____.