Exam 8: Statistical Inference: Estimation for Single Populations

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

Suppose a random sample of 36 is selected from a population with a standard deviation of 12.If the sample mean is 98,the 90% confidence interval for the population mean is ___.

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

A researcher wants to estimate the population proportion with a 90% level of confidence.She estimates from previous studies that the population proportion is no more than .30.The researcher wants the estimate to have an error of no more than .02.The necessary sample size is 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 45 randomly selected walk-in customers,and calculated that their mean waiting time was 15 minutes.If Brian concludes that the average waiting time for all walk-in customers is 15 minutes,he is using a ___.

Estimate a population proportion using the z statistic.

A researcher wants to estimate the proportion of the population which possesses a given characteristic.A random sample of size 800 is taken resulting in 360 items which possess the characteristic.The point estimate for this population proportion 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 t distribution is similar to a normal distribution,but flatter in the middle.

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 ___.

Elwin Osbourne,CIO at GFS,Inc. ,is studying employee use of GFS email for non-business communications.He plans to use a 95% confidence interval estimate of the proportion of email messages that are non-business;he will accept a 0.05 error.Previous studies indicate that approximately 30% of employee email is not business related.Elwin should sample ___ email messages.

James Desreumaux,VP of Human Resources of Maritime Boat Manufacturing (MBM),is reviewing the employee training programs of MBM factories.His staff randomly selected personnel files for 10 workers in Nova Scotia,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 ___.

Velma Vasquez,fund manager of the Vasquez Value Fund,manages a portfolio of 250 common stocks.Velma relies on various statistics,such as variance,to assess the overall risk of stocks in an economic sector.Her staff reported that for a sample 14 utility stocks the mean annualized return was 14% and that the variance was 3%.Assume that annualized returns are normally distributed.The 95% confidence interval for the population variance of annualized returns is ___.

A study will be conducted to estimate the population proportion.A level of confidence of 99% will be used and an error of no more than .04 is desired.There is no knowledge as to what the population proportion will be.The size of sample should be at least ___.

James Desreumaux,VP of Human Resources of Maritime Boat Manufacturing (MBM),is reviewing the employee training programs of MBM factories.His staff randomly selected personnel files for 100 workers in New Brunswick 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 ___.

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.

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

If the population is not normal but its standard deviation,σ,is known and the sample size,n is large (n ≥ 30),z-distribution values may be used to determine interval estimates for the population mean.

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