Margin of Error and Confidence Level

An IQ test was given to a simple random sample of 75 students at a certain college. The sample mean score was 105.2. Scores on this test are known to have a standard deviation of 10. It is desired to construct a 90% confidence interval for the mean IQ scores of the students at the college. Find the critical value.

• 0.90

• 1.155

• 1.645

• ±1.645

The larger your confidence interval is, the more sure (higher confidence level) you can be.

• True

• False

Complete the equation: 
point estimate +/- _____

• standard deviation

• margin of error

• critical value

• confidence level

What can you do to reduce the margin of error? 

• increase the confidence level

• decrease the confidence level

• increase sample size

• decrease sample size

Which of the following is an example of an interval estimate?

• point estimate 

• critical value

• confidence interval

• statistic

What is the critical value z* for a 99% confidence interval? 

• -2.58

• 1.96

• -1.64

• 2.58

Construct a 90% confidence interval of a random sample size of 19 cows with a mean of 155.526 and a standard deviation of 19.993. 

• (146.54, 164.52)

• (147.57, 163.48)

• (147.59, 163.46)

• (143.69, 167.36)

What can be inferred about the relationship between confidence level and margin of error?

• Increasing the confidence level decreases the margin of error.

• Increasing the confidence level increases the margin of error.

• The confidence level and margin of error are not related.

• Decreasing the confidence level decreases the margin of error.

If the margin of error in a confidence interval is 4, what is the range of the confidence interval around a sample mean of 50?

• 46 to 54

• 48 to 52

• 45 to 55

• 49 to 51

If you increase the confidence level from 90% to 95%, what happens to the margin of error?

• It decreases.

• It stays the same.

• It increases.

• It becomes zero.