Proportion Confidence Intervals

Identify the confidence interval used in the figure below if each shaded area is equal to 0.05.

• 90%
• 95%
• 98%
• 99%

To find a z-score, use InvNorm(1-c).

• True
• False

The confidence level of an interval estimate of a parameter is the probability that the interval estimate will contain the parameter.

• True
• False

The symbol for the sample proportion is __________.

• Z_c
• p̂
• E
• q

A research company wants to estimate the proportion of people who like oatmeal.  They want the confidence level to be 95%.  The company gets 325 people to sign up for the survey, but on the day that the survey is issued, only 250 people show up and take the survey.  What happens to the confidence interval?

• It gets larger
• It gets smaller
• It stays the same
• Too little information given

Find the value of z_c for a 90% confidence interval.

• -1.96 
• 1.645
• 1.440
• -1.598

The __________ is the maximum likely difference between the point estimate of a parameter and the actual value of the parameter.

• Point Estimate
• Inference
• Confidence Level
• Maximum Error of Estimate

A sample of 400 racing cars showed that 80 cars cost over $700,000. What is the 99% confidence interval of the true proportion of cars costing over $700,000?

• 0.001 < p < 0.005
• 0.566 < p < 0.693
• 0.148 < p < 0.252
• 0.023 < p < 0.045

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