A medical researcher treats 400 subjects with the high cholesterol with a new drug. The average decrease in cholesterol level is = 90 after two months of taking the drug. Assume that the decrease in cholesterol after two months of taking the drug follows a Normal distribution, with unknown mean ? and standard deviation ? = 30.
Which of the following would produce a confidence interval with a smaller margin of error than the 95% confidence interval you computed above?
A. Give the drug to only 100 subjects rather than 400, since 100 people are easier to manage and control.
B. Give the drug to 500 subjects rather than 400.
C. Compute a 99% confidence interval rather than a 95% confidence interval. The increase in confidence indicates that we have a better interval.
D. None of the above