Exam 8: Sampling Distributions and Estimation

In constructing a confidence interval for a mean with unknown variance with a sample of 25 items,Beth used z instead of t."Well,at least my interval will be wider than necessary,so it was a conservative error," said she.Is Beth's statement correct?

List differences and similarities between Student's t and the standard normal distribution.

What is the approximate width of an 80 percent confidence interval for the true population proportion if there are 12 successes in a sample of 80?

In constructing a 95 percent confidence interval,if you increase n to 4n,the width of your confidence interval will be (assuming other things remain the same)

Why does σ pose a problem for sample size calculation for a mean? How can σ be approximated when it is unknown?

A random sample of 160 commercial customers of PayMor Lumber revealed that 32 had paid their accounts within a month of billing.Can normality be assumed for the sample proportion?

We could narrow a 95 percent confidence interval by

A 90 percent confidence interval will be wider than a 95 percent confidence interval,ceteris paribus.

A 95 percent confidence interval constructed around p will be wider than a 90 percent confidence interval.

A random sample of 16 ATM transactions at the Last National Bank of Flat Rock revealed a mean transaction time of 2.8 minutes with a standard deviation of 1.2 minutes.The width (in minutes)of the 95 percent confidence interval for the true mean transaction time is

The confidence level refers to the procedure used to construct the confidence interval,rather than to the particular confidence interval we have constructed.

All estimators are biased since sampling error always exists to some extent.

For a sample of size 16,the critical values of chi-square for a 95 percent confidence interval for the population variance are

If σ = 12,find the sample size to estimate the mean with an error of ± 4 and 95 percent confidence (rounded to the next higher integer).

In constructing a confidence interval for a mean,the width of the interval is dependent on the sample size,the confidence level,and the population standard deviation.

A poll showed that 48 out of 120 randomly chosen graduates of California medical schools last year intended to specialize in family practice.What is the width of a 90 percent confidence interval for the proportion that plan to specialize in family practice?

The Central Limit Theorem implies that

A higher confidence level leads to a narrower confidence interval,ceteris paribus.

As the sample size increases,the standard error of the mean

To estimate the average annual expenses of students on books and class materials,a sample of size 36 is taken.The sample mean is $850 and the sample standard deviation is $54.A 99 percent confidence interval for the population mean is