Exam 8: Statistical Inference: Estimation for Single Populations

Catherine Chao,Director of Marketing Research,is evaluating consumer acceptance of a new toothpaste package. Her staff reports that 17% of a random sample of 200 households prefers the new package to all other package designs. If Catherine concludes that 17% of all households prefer the new package,she is using _______.

Eugene Gates,Marketing Director of Mansfield Motors Manufacturers,Inc.'s Electrical Division,is leading a study to assess the relative importance of product features.An item on a survey questionnaire distributed to 100 of Mansfield's customers asked them to rate the importance of "ease of maintenance" on a scale of 1 to 10 (with 1 meaning "not important" and 10 meaning "highly important").His staff assembled the following statistics. If Eugene concludes that the average rate of "ease of maintenance" for all customers is 7.5,he is using ________.

A researcher wants to estimate the proportion of manufacturing companies that use the "six sigma" method.For this purpose,she takes a random sample of 50 manufacturing companies and finds out that 28 of them employ this method.The point estimate for the proportion of the population that uses this method is ______.

The t score (or table value for Student's t distribution)associated with the upper 5% and 48 degrees of freedom is ______.

The z value associated with a two?sided 90% confidence interval 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 95% confidence interval for the population mean weight of a semi tracker truck is ______________.

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 100 tellers in the Southeast Region and determined that their mean training time was 25 hours. Assume that the population standard deviation is 5 hours. The 88% confidence interval for the population mean of training times is ________.

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 100 tellers in the Southeast Region and determined that their mean training time was 25 hours. Assume that the population standard deviation is 5 hours. The 92% confidence interval for the population mean of training times is ________.

A market researcher computed a confidence interval for a population proportion using a 95% confidence level.Her boss decided that she wanted a 99% confidence level instead.The new interval with 99% confidence level will be wider than the original one with a 95% confidence level.

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 90% 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 .02. The necessary sample size is at least _______.

Use of the chi-square statistic to estimate the population variance is extremely robust to the assumption that the population is normally distributed.

Elwin Osbourne,CIO at GFS,Inc.,is studying employee use of GFS e-mail for non-business communications.He plans to use a 98% confidence interval estimate of the proportion of e-mail messages that are non-business; he will accept a 0.05 error. Previous studies indicate that approximately 30% of employee e-mail is not business related.Elwin should sample _______ e-mail messages.

Life tests performed on a sample of 13 batteries of a new model indicated: (1)an average life of 75 months,and (2)a standard deviation of 5 months. Other battery models,produced by similar processes,have normally distributed life spans. The 98% confidence interval for the population mean life of the new model is _________.

Suppose a random sample of 16 is selected from a population with a normal distribution with a known population standard deviation σ of 10.Assume that the sample mean is 4.2.Based on a 90% confidence interval for the population mean,we can conclude that 0.1 is a plausible number for the population mean μ.

In estimating the sample size necessary to estimate p,if there is no good approximation for the value of p available,the value of ____ should be used as an estimate of p in the formula.

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 100 tellers in the Southeast Region and determined that their mean training time was 25 hours. Assume that the population standard deviation is 5 hours. The 95% confidence interval for the population mean of training times is ________.

A random sample of 225 items from a population results in 60% possessing a given characteristic.Using this information,the researcher constructs a 90% confidence interval to estimate the population proportion.The resulting confidence interval is _______.

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

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 ________.

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