Intro to Confidence Intervals

A recent survey found that out of 400 random American adults, 89% pay their bills on time. The margin of error in this survey was 2%. What is the interval of values in which the truth is likely found?

• 89% - 91%

• 87% - 89%

• 87% - 91%

• 388 - 402

How do we reduce variability?

• Increase randomness.

• Increase sample size.

• Decrease randomness.

• Decrease sample size.

Why is a sample of 1000 people better than a sample of 100 people?

• It reduces the margin of error.

• It decreases bias.

• Having more people is always better.

• More people means that our results are more accurate.

A recent survey found that 77% of high schoolers use their phones more than 4 hours a day on average. The margin of error was 3%. What is the interval for which we could expect to find the truth of the population?

• 77% - 80%

• 74% - 77%

• 74% - 80%

• 50 million high schoolers - 120 million

Increasing the sample size __________ the confidence interval. 

• increases
• decreases
• does not affect
• there is not enough evidence to determine the answer

Given the interval (1.2, 1.8), what is the point estimate and the margin of error? 

• 1.5, 0.6
• 1.5, 0.3
• 1.2, 0.3
• 1.2, 0.6

The amount added and subtracted to the statistic.

• Margin of Error

• Point Estimator

• Statistic

• Population

What is the point estimator for the interval (5 , 13)?

• 10

• 9.5

• 9

• -5

What is the margin of error for the interval (6.8, 12.9)?

• 9.85

• 3.05

• 3.50

• 6.8

Does the interval (3, 14) support the claim that the mean of a data set is 2.9

• Yes

• No

• Not enough information.