Exam 8: Statistical Inference: Estimation for Single Populations

The normal distribution is used to test about a population mean for large samples if the population standard deviation is known. "Large" is usually defined as _______.

A researcher wants to estimate the proportion of the population which possesses a given characteristic.A random sample of size 1800 is taken resulting in 450 items which possess the characteristic.The point estimate for this population proportion is _______.

The z value associated with a two?sided 80% confidence interval is _______.

If the degrees of freedom in a t distribution increase,difference between the t values and the z values will also increase.

You are thinking of using a t-table to find a 95 percent confidence interval for the mean μ of a population.The distribution of the population is normal and the population standard deviation is unknown.A random sample of size n is drawn from this population.You may use the t-distribution only if the sample size n is small.

Elwin Osbourne,CIO at GFS,Inc.,is studying employee use of GFS e-mail for non-business communications. A random sample of 200 e-mail messages was selected. Thirty of the messages were not business related.The 98% confidence interval for the population proportion is _________.

Elwin Osbourne,CIO at GFS,Inc.,is studying employee use of GFS e-mail for non-business communications. A random sample of 200 e-mail messages was selected. Thirty of the messages were not business related.The 90% confidence interval for the population proportion is _________.

A researcher wants to estimate the percent of the population that uses the internet to stay informed on world news issues.The researcher wants to estimate the population proportion with a 98% level of confidence. He estimates from previous studies that at least 65% of the population stay informed on world issues through the internet..He also wants the error to be no more than .03.The sample size should be at least _______.

An assumption underlying the use of t-statistic in sample-based estimation is that the population is normally distributed.

Catherine Chao,Director of Marketing Research,is evaluating consumer acceptance of a new toothpaste package. She randomly selects a sample of 200 households. Forty households prefer the new package to all other package designs. The 90% confidence interval for the population proportion is _________.

Suppose a researcher is interested in understanding the variation in the price of store brand milk.A random sample of 36 grocery stores selected from a population and the mean price of store brand milk is calculated.The sample mean is $3.13 with a standard deviation of $0.23.Construct a 99% confidence interval to estimate the population mean.

A researcher is interested in estimating the mean weight of a semi tracker truck to determine the potential load capacity.She takes a random sample of 17 trucks and computes a sample mean of 20,000 pounds with sample standard deviation of 1,500.She decides to construct a 98% confidence interval to estimate the mean.The degrees of freedom associated with this problem are _______.

The z value associated with a two?sided 95% confidence interval is _______.

Catherine Chao,Director of Marketing Research,is evaluating consumer acceptance of a new toothpaste package. She plans to use a 95% confidence interval estimate of the proportion of households which prefer the new packages; she will accept a 0.05 error. Previous studies indicate that new packaging has an approximately 70% acceptance rate.The sample size should be at least _______.

Brian Vanecek,VP of Operations at Portland Trust Bank,is evaluating the service level provided to walk-in customers. Accordingly,his staff recorded the waiting times for 64 randomly selected walk-in customers and determined that their mean waiting time was 15 minutes. Assume that the population standard deviation is 4 minutes. The 95% confidence interval for the population mean of waiting times is ________.

The employees of Cybertronics Inc.need to complete a certification online.A random sample of 49 employees gives an average time for completion of all the coursework and passing the tests of 6 hours.Assume that the population standard deviation is 6 hours and the population of employees is fairly large.Construct a 95% confidence interval for the average time required to complete the certification.

James Desreumaux,VP of Human Resources of American First Banks (AFB),is reviewing the employee training programs of AFB banks. His staff randomly selected personnel files for 10 tellers in the Southwest Region,and determined that their mean training time was 25 hours and that the standard deviation was 5 hours. Assume that training times are normally distributed. The 90% confidence interval for the population variance of training times is ________.

Brian Vanecek,VP of Operations at Portland Trust Bank,is evaluating the service level provided to walk-in customers. Accordingly,his staff recorded the waiting times for 64 randomly selected walk-in customers and determined that their mean waiting time was 15 minutes. Assume that the population standard deviation is 4 minutes. The 90% confidence interval for the population mean of waiting times is ________.

A random sample of 64 items is selected from a population of 400 items.The sample mean is 200. The population standard deviation is 48.From this data,a 90% confidence interval to estimate the population mean can be computed as _______.

Suppose a researcher is interested in understanding the variation in the price of store brand milk.A random sample of 36 grocery stores selected from a population and the mean price of store brand milk is calculated.The sample mean is $3.13 with a standard deviation of $0.23.Construct a 95% confidence interval to estimate the population mean.