Exam 8: Statistical Inference: Estimation for Single Populations

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.

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 ___.

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 90% confidence interval to estimate the population mean can be computed as ___.

The weights of aluminum castings produced by a process are normally distributed.A random sample of 5 castings is selected; the sample mean weight is 2.21 kilograms; and the sample standard deviation is 0.12 kilograms.The 98% confidence interval for the population mean casting weight is ___.

The z value associated with a two-sided 95% confidence interval is ___.

Given n = 12, s² = 44.90, and that the population is normally distributed, the 99% confidence interval for the population variance is ___.

Given n = 17, s² = 18.56, and that the population is normally distributed, the 80% confidence interval for the population variance is ___.

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

Suppose a random sample of size 64 is selected from a population yielding a sample mean of 26.The population standard deviation is 4.From this information, the 90% confidence interval to estimate the population mean can be computed to be ___.

A researcher wants to estimate the proportion of a population which possesses a given characteristic.A random sample of size 250 is taken and 40% of the sample possesses the characteristic.The 95% confidence interval to estimate the population proportion is ___.

The z value associated with a two-sided 88% confidence interval 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 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 ___.

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

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.

A researcher wants to estimate the population proportion with a 95% level of confidence.He 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 .03.The necessary sample size is at least ___.