Chapter 8

Interval Estimates for Proportions, Mean Differences and Proportion Differences

Question 1

Suppose you construct a confidence interval for the difference between two population proportions. All other things equal, the confidence interval will necessarily be wider

A. the sample sizes are larger

B.the confidence level is larger

C.the difference between the sample proportions is larger

D. the sample proportions are known

Question 2

The sampling distribution of the sample proportion is can be treated as a normal distribution when which of the following conditions holds?

a)n(pi) > 5

b)n(1 -pi) > 5

c)pihas a uniform distribution

d)both a and b

Question 3

Four economists have made economic forecasts for next year. Three forecast a downturn, one forecast an upturn.

Economist W X Y Z

Forecast Down Up Down Down

List the 4 possible samples of size 3 that could be selected from this population of economists.

A.WXY, WXZ, WYX, XYZ

B.WXY, WXZ, WYZ, XYW

C.WZY, WXZ, WYZ, XYZ

D.WXY, WXZ, WYZ, XYZ

Question 4

Before-and-after experiments in which the same subjects are observed before and after a particular treatment are a good illustration of

A. matched samples.

B. time-sensitive data.

C. non-traditional statistical methods.

D. 100% sampling.

Question 5

You want to estimate the proportion of households in the Portland area that have no landline telephone service. Suppose you plan to take a simple random sample of Portland households and target a margin of error no larger than plus or minus .02 for a proposed 90% confidence interval estimate. How large a sample would you recommend? (Assume you have no prior information about the likely population proportion.)

A. 1026

B. 1702

C. 3425

D. 1322

Question 6

Estimates vary widely as to the prevalence of cheating on campus. You plan to administer an anonymous survey to estimate the proportion of students who have cheated on a test in the past year. At a 95% confidence level, you would like your estimate to have a margin of error no greater than 3%. How large a sample should you take to ensure that you achieve your target margin of error?

A. 267 students

B. 757 students

C. 1068 students

D. Insufficient information is given to determine the necessary sample size

Question 7

A Seattle Times poll of 503 voters found that 30% of those surveyed favored the incumbent mayor in Seattle's upcoming mayoral election. Using a 95% confidence level, the margin of error for the poll result was reported to be 4.5% (Seattle Times, September 2013). Choose the best interpretation of this poll result.

A. The share of the sample that favors the incumbent mayor is between 25.5% and 34.5%, with 95% confidence.

B. The share of voters that favors the incumbent mayor is between 25.5% and 34.5%, with 95% confidence.

C. There is a 95% chance that support for the mayor will be between 25.5% and 34.5% in the upcoming election.

D. There is a 95% chance that 30% of voters currently favor the mayor in the upcoming election.