Chapter 8: Problem 7
Briefly explain the difference between a confidence level and a confidence interval.
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Chapter 8: Problem 7
Briefly explain the difference between a confidence level and a confidence interval.
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What is the point estimator of the population mean, \(\mu\) ? How would you calculate the margin of error for an estimate of \(\mu\) ?
When one is attempting to determine the required sample size for estimating a population mean, and the information on the population standard deviation is not available, it may be feasible to take a small preliminary sample and use the sample standard deviation to estimate the required sample size, \(n .\) Suppose that we want to estimate \(\mu\), the mean commuting distance for students at a community college, to a margin of error within 1 mile with a confidence level of \(95 \%\). A random sample of 20 students yields a standard deviation of \(4.1\) miles. Use this value of the sample standard deviation, \(s\), to estimate the required sample size, \(n .\) Assume that the corresponding population has an approximate normal distribution.
A city planner wants to estimate the average monthly residential water usage in the city. He selected a random sample of 40 households from the city, which gave a mean water usage of \(3415.70\) gallons over a 1-month period. Based on earlier data, the population standard deviation of the monthly residential water usage in this city is \(389.60\) gallons. Make a \(95 \%\) confidence interval for the average monthly residential water usage for all households in this city.
According to the 2015 Physician Compensation Report by Medscape (a subsidiary of WebMD), American orthopedists earned an average of \(\$ 421,000\) in 2014 . Suppose that this mean is based on a random sample of 200 American orthopaedists, and the standard deviation for this sample is \(\$ 90,000\). Make a \(90 \%\) confidence interval for the population mean \(\mu\).
Determine the sample size for the estimate of \(\mu\) for the following. a. \(E=.17, \quad \sigma=.90\), confidence level \(=99 \%\) b. \(E=1.45, \quad \sigma=5.82, \quad\) confidence level \(=95 \%\) c. \(E=5.65, \quad \sigma=18.20, \quad\) confidence level \(=90 \%\)
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