Exam 8: Statistical Inference: Estimation for Single Populations

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 _________.

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.The 90% confidence interval for the population mean rod length is ______________.

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

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.The 95% confidence interval for the population mean weight of a semi tracker truck is ______________.

A researcher wants to determine the sample size necessary to adequately conduct a study to estimate the population mean to within 5 points.The range of population values is 80 and the researcher plans to use a 90% level of confidence.The sample size should be at least _______.

A researcher wants to estimate the percent of the population that uses the radio to stay informed on local news issues.The researcher wants to estimate the population proportion with a 95% level of confidence.He estimates from previous studies that no more than 30% of the population stay informed on local issues through the radio.The researcher wants the estimate to have an error of no more than .03.The necessary sample size is at least _______.

When a statistic calculated from sample data is used to estimate a population parameter,it is called a point estimate.

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 92% confidence interval to estimate the population mean..

When a range of values is used to estimate a population parameter,it is called a range estimate.

Like a t-distribution,a chi-square distribution is symmetrical and extends from minus infinity to plus infinity.

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 95% confidence interval for the population variance of training times is ________.

The table t value associated with the upper 5% of the t distribution and 12 degrees of freedom is _______.

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 _______.

Given n = 20,s = 32,and that the population is normally distributed,the 90% confidence interval for the population variance is ________.

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 point estimate for this population proportion 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 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 _______.

If the population is normal and its standard deviation,,is known and the sample size,n,is large (n ≥ 30),interval estimates for the population mean must be determined using z-values.

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

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 _______.