Exam 7: Statistical Inference: Estimating a Population Mean

Suppose a random sample of 40 online retailers is selected to estimate the average price of a particular item.The average price in the sample is $1.38.Build a 99% confidence interval estimate of the average price of the item for the population of online retailers represented here.Assume the standard deviation of prices for the population of retailers who sell the item is known to be $.22.Report the upper bound for your interval.

The normal approximation to the t distribution is commonly used:

Which of the following is a key property of the sampling distribution of the sample mean?

From a population that is normally distributed with an unknown standard deviation, a sample of size 20 elements is selected.To construct an interval estimate of the population mean, the proper distribution to use is the:

In a random sample of 25 calls made from the U.S.to Japan by callers using Skype during the past week, the average call lasted 21.4 minutes, with a sample standard deviation of 5.1 minutes.Assume the population distribution of call times is normal.Build a 99% confidence interval estimate of the average call time for the population of calls represented by the sample (that is, the population of all calls made from the US to Japan last week by callers using Skype).Report the upper bound for your interval.

Chen Inc.wants to estimate the average processing time for 2000 current orders.You take a simple random sample of 40 orders, and determine the average processing time required for the orders in the sample is 6.5 hours, with a sample standard deviation of 1.6 hours.Build the 95% confidence interval estimate of average processing time for the population of 2000 orders.Show the upper bound for your interval.

A random sample is a sample selected according to the laws of chance and in a way that gives every member of the population a measurable, non-zero probability of being included.

Crownfashions.com wants to estimate the average time that visitors to its website spend browsing the site.In a random sample of 49 visits this week, average browsing time is 13.6 minutes.Assume you know the population standard deviation is 5.2 minutes.Construct a 95% confidence interval estimate of average browsing time for the population of crownfashion.com visitors this week.Report the upper bound for your interval.

The sampling distribution of the sample mean is the probability distribution of all possible values of the sample mean when samples of size n are taken from a given population.

In telephone interviews with a random sample of 1,100 online shoppers, shoppers said they expected to spend an average of $976 for online purchases this year.Using a sample standard deviation of $180, you build a 95% confidence interval estimate of the average spending for the population of online shoppers represented by the sample and determine the margin of error for your 95% interval.Now suppose you want to reduce the margin of error in your interval by 20% without sacrificing the 95% confidence level.How big a sample would be required?

The purpose of statistical inference is to provide information about the:

The finite population correction factor (fpc) is required in the formula for the standard error whenever n/N < .10.

A finite population correction (fpc) factor increases the size of the standard error of the mean when sampling is done without replacement from a finite population.

A simple random sample of size n from a population of size N is a sample selected such that each possible sample of size n has a probability of 0.5 of being selected.

You want to build a 90% confidence interval estimate of a population mean.You take a sample of size 100 and find a sample mean of 1300.If the population standard deviation is 25, calculate the standard error of the sampling distribution of the sample mean.

Intervals constructed using a __________ to collect a given percentage of values will be wider than comparable intervals constructed using a __________.

You want to build a 95% confidence interval estimate of the mean of a large population.You want the margin of error to be no more than 3.You estimate that the population standard deviation is 42.How big a sample should you select?

Which of the following statements is TRUE about the Central Limit Theorem?

Which of the following is a factor that influences interval width?

Clatsop Retailing Inc.owns four stores in the Plainfield, New Jersey, area.The company plans to choose a sample of two of these stores to test a new store layout.If we identify the stores as Store A, Store B, Store C and Store D, list all six equally likely samples of size 2 that could be selected if Clatsop uses simple random sampling without replacement.