7. Why is a confidence interval also called a "margin of error"?

9. A researcher wants to construct a 99% confidence interval for the proportion of Americans who think that the U.S. invading Iraq was an effective step in combating world terrorism. She has no initial idea of what that proportion is. How large should her sample size be if she wants the margin of error to be at most two percent? Show or explain your thinking.

Suppose we know that a confidence interval for a population proportion is (0.105,0.355), with a sample proportion of p̂=0.23. What is the margin of error?

You are trying to study the level of personal net worth of a low income populaon. In parcular you are interested in find the confidence interval of the mean level of net worth (net worth can be posive or negave and is measured in thousands of dollars). You do not know the distribuon of the level of net worth of the populaon. For your study, you collected a sample from 100 persons asking them their level of net worth. The results were such that the sample meanXˉ = 3 and the sample variance Sn2 = 100 (Assume you choose the persons randomly, they report their true net worth, and the populaon is sufficiently large.) From this data, find the 90% confidence interval of the mean level of net worth.(Do not use t distribuon)

Please help with A and B

23)   It is found that a 95% confidence interval for the mean score of all students on an aptitude test is (62, 70). It means that there is a 95% chance that the mean score of all students on an aptitude test is between 62 and 70.     False     True

What happens to the interval width as confidence level increases? Why?

Why is it that when we increase our confidence level in a confidence interval that the interval gets wider?

explain the logic behind why confidence intervals with higher confidence levels are wider than others?