Exam 8: Statistical Inference: Estimation for Single Populations

A researcher is interested in estimating the mean weight of a semi tractor 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 tractor truck is ______________.

A researcher wants to estimate the proportion of manufacturing companies that use the six sigma method.For this purpose, she will take a random sample of 50 manufacturing companies and find out how many of them use this method.She estimates that the proportion will be anywhere from 0.4 to 0.55.Of all the proportions in that range, which one would produce the widest 95% confidence interval for the population proportion?

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 _______.

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

The table t value associated with the upper 5% of the t distribution and 14 degrees of freedom is _______.

The table t value associated with the upper 10% of the t distribution and 23 degrees of freedom is _______.

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

Elwin Osbourne, CIO at GFS, Inc., is studying employee use of GFS e-mail for non-business communications.He plans to use a 95% 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.

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

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 _______.

In order to find values in the t distribution table, you must determine the appropriate degrees of freedom based on the sample sizes.

If you need to estimate the population mean within 2.5 units and with a confidence level of 95%.The minimum value observed is 15 and the maximum, 65.What sample size would you use?

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

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

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 ________.

An assumption underlying the use of t-statistic in sample-based estimation is 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 approximately _______ e-mail messages.

A researcher wants to estimate the proportion of Millennials who regularly listen to podcasts (defined as at least two entire podcasts per week).Previous studies indicate that only 18% of Millennials listen regularly to podcasts, and this researcher wants to estimate if that figure has increased.For this purpose, the researcher will use a 98% confidence level and wants to estimate the population proportion within 0.05 (i.e., 5 percentage points)of the actual value.The approximate sample size is at least ______.

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 these data, the 90% confidence interval to estimate the population mean would be _______.

If the standard deviation, σ is known the z-distribution values may not be used to determine interval estimates for the population mean when