Exam 9: Estimation and Confidence Intervals

Deciding on the number of observations to include in a sample is an important decision when planning a research study. What information is required to make this decision?

When we use a confidence interval to reach a conclusion about the population mean, we are applying a type of reasoning or logic called __________.

A local politician wants an estimate of the proportion of the population who support her fiscal policies. She wants the estimate to be within .06 of the true proportion. Assume a 95% level of confidence. The politician's advisors estimated the proportion supporting her fiscal policy to be .60. How large of a sample is required?

To compute a confidence interval for a population proportion, a __________ statistic is used.

A sample of 2,000 union members was selected, and a survey recorded their opinions regarding a proposed management union contract. A total of 1,600 members were in favor of it. A 95% confidence interval estimated that the population proportion was between 0.78 and 0.82. This indicates that about 80 out of 100 similarly constructed intervals would include the population proportion.

A local grocery store wants to estimate the mean daily number of gallons of milk sold to customers. Assume the number of gallons sold follows the normal distribution, with a population standard deviation of 5.10 gallons. A random sample of 60 days shows that the mean daily number of gallons sold is 10.00. What is the point estimate of the population mean?

A group of statistics students decided to conduct a survey at their university to find the average (mean) amount of time students spent studying per week. Assuming a population standard deviation of six hours, what is the required sample size if the error should be less than a half hour with a 95% level of confidence?

A student wanted to construct a 99% confidence interval for the mean age of students in her statistics class. She randomly selected nine students. Their mean age was 19.1 years with a sample standard deviation of 1.5 years. What is the 99% confidence interval for the population mean?

There are 250 computer programmers employed at Computers.com, Inc. A sample of 50 programmers revealed that 30 graduated with a four-year college degree. Construct the 95 percent confidence interval for the proportion of all programmers who graduated from a four-year university.

A research firm conducted a survey to determine the mean amount people spend at a popular coffee shop during a week. They found the amounts spent per week followed a normal distribution with a population standard deviation of $4. A sample of 64 customers revealed that the mean is $25. What is the 99% confidence interval estimate of µ?

A consultant is planning a survey of corporate executives to determine their mean amount of weekly work time. A pilot survey indicated that the mean work time per week is 50 hours, with a standard deviation of 10 hours. The consultant wants to estimate the mean weekly work time within five hours. The 95% level of confidence is to be used. How many executives should be surveyed?