Finding Confidence Intervals for Mean and Proportions

Which of the following changes to a study would result in a narrower confidence interval?

• increasing the confidence level, increasing the sample size
• decreasing the confidence level, decreasing the sample size
• increasing the confidence level, decreasing the sample size
• decreasing the confidence level, increasing the sample size.

A recent study of 750 Internet users in Europe found that 35% of Internet users were women.  What is the 95% confidence interval of the true proportion of women in Europe who use the Internet? 

• 0.321 < p < 0.379
• 0.316 < p < 0.384
• 0.309 < p < 0.391
• 0.305 < p < 0.395

A survey of 800 women shoppers found that 17% of them shop on impulse.  What is the 98% confidence interval for the true proportion of women shoppers who shop on impulse? 

• 0.148 < p < 0.192
• 0.136 < p < 0.204
• 0.144 < p < 0.196
• 0.139 < p < 0.201

A researcher at a major hospital wishes to estimate the proportion of the adult population of the U.S. that has high blood pressure.  How large a sample is needed in order to be 90% confident that the sample proportion will not differ from the true proportion by more than 5%?

• 9
• 271
• 164
• 542

It was found that in a sample of 90 teenage boys, 70% of them have received speeding tickets.  What is the 90% confidence interval of the true proportion of teenage boys who have received speeding tickets? 

• (0.621, 0.780)
• (0.591, 0.812)
• (0.584, 0.830)
• (0.615, 0.805)

Which of the following values below represents the critical value for a 98% confidence interval?

• 2.326
• 2.054
• 1.645
• 3.091

Which of the following is the definition of a "point estimate?"

• The average of a population.

• The average of a sample.

• The midpoint of a confidence interval.

• The confidence interval.

The amount added and subtracted to the statistic.

• Margin of Error

• Point Estimator

• Statistic

• Population

Which of the following sources of error is included in the margin of error

• chance variation in choosing a random sample.
• undercoverage.
• some of the subjects did not understand the questions.
• voluntary response.

The 99% confidence interval for a proportion is (0.54, 0.72). What is p̂?

• 0.63
• 0.18
• 0.09
• 0.66