Exam 9: Estimation and Confidence Intervals

Recently, a university surveyed recent graduates of the English Department for their starting salaries. Four hundred graduates returned the survey. The average salary was $25,000 with a standard deviation of $2,500. What is the best point estimate of the population mean?

A group of statistics students decided to conduct a survey at their university to estimate the average (mean) amount of time students spent studying per week. They sampled 554 students and found a mean of 22.3 hours per week. Assuming a population standard deviation of 6 hours, what is the 95% level of confidence?

A 95 percent confidence interval implies that about 95 out of 100 similarly constructed intervals will include the _____________ being estimated.

When deciding on the number of observations to include in a sample, what would favor larger sample sizes?

A survey of households in a small town showed of 1200 sampled households, that in 500 households at least one member attended a town meeting during the year. Using the 95% level of confidence, what is the confidence interval for the proportion of households represented at a town meeting?

In terms of the standard error of the mean, how wide is a 90 percent confidence interval? ______

A sample of 2000 union members was selected and their opinions regarding a proposed management union contract were recorded. 1,600 members were in favor of it. A 95% confidence interval for the population proportion was computed to be 0.78 and 0.82. This indicates that about 80 out of 100 similarly constructed intervals would include the population proportion.

The finite population correction factor is used to adjust the z-statistic.

The t distribution is based on the assumption that the population of interest is normal or nearly normal.

A local retail company wants to estimate the mean amount spent. Their budget limits the number of surveys to 225. What is their maximum error of the estimated mean amount spent for a 99% level of confidence and an estimated standard deviation of $10.00?

A confidence interval is narrower when the confidence level __________________.

When using Student's t to compute an interval estimate,

A confidence interval for a population mean

To determine the size of a sample, the standard deviation of the population must be estimated by either taking a pilot survey or by approximating it based on knowledge of the population.

To determine the value of the standard error of the mean, the total error is divided by the sample size.

If 95% and 98% confidence intervals were developed to estimate the true cost of a MP3 player microwave, what differences would they have?

Thirty-six items are randomly selected from a population of 150 items. The sample mean is 25 and the sample standard deviation 3. What is the adjusted standard error of the mean?

What happens to the computed value of t as the sample size increases? ______________

Which statement(s) is/are correct about the t distribution?

To compute a confidence interval, a __________ is used when the population standard deviation is known.