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.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 ___.

A random sample of 225 items from a population results in 60% possessing a given characteristic.Using this information, the researcher constructs a 99% confidence interval to estimate the population proportion.The resulting confidence interval 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 ___.

A researcher wants to estimate the proportion of a population which possesses a given characteristic.A random sample of size 200 is taken and 30% of the sample possesses the characteristic.The 95% confidence interval to estimate the population proportion is ___.

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 ___.

A researcher wants to estimate the proportion of a population which possesses a given characteristic.A random sample of size 200 is taken and 30% of the sample possesses the characteristic.The 90% confidence interval to estimate the 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 95% confidence interval for the population mean of waiting times is ___.

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 92% confidence interval for the population mean 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 90% confidence interval for the population variance of annualized returns is ___.

Brian Vanecek, VP of Operations at Portland Trust Bank, is evaluating the service level provided to walk-in customers.Brian would like to minimize the variance of waiting time for these customers, since this would mean each customer received the same level of service.Accordingly, his staff recorded the waiting times for 15 randomly selected walk-in customers, and determined that their mean waiting time was 15 minutes and that the standard deviation was 4 minutes.Assume that waiting time is normally distributed.The 90% confidence interval for the population variance 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 95% confidence interval to estimate the population mean can be computed as ___.

A researcher is interested in estimating the mean value for a population.She takes a random sample of 17 items and computes a sample mean of 224 and a sample standard deviation of 32.She decides to construct a 98% confidence interval to estimate the mean.The degrees of freedom associated with this problem are ___.

When the population standard deviation, σ, is unknown the sample standard deviation, s, is used in determining the interval estimate for the population mean.

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 ___.

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 ___.

A study is going to be conducted in which a population mean will be estimated using a 92% confidence interval.The estimate needs to be within 12 of the actual population mean.The population variance is estimated to be around 2500.The necessary sample size should be at least ___.

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.

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

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 ___.

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.