9.16 In a survey on supernatural experiences, 722 of 4013 adult Americans surveyed reported that they had seen or been with a ghost (“What Supernatural Experiences We’ve Had,” USA Today, February 8, 2010).

a. What assumption must be made in order for it to be appropriate to use the formula of this section to construct a confidence interval to estimate the proportion of all adult Americans who have seen or been with a ghost?

b. Construct and interpret a 90% confidence interval for the proportion of all adult Americans who have seen or been with a ghost. (Hint: See Example 9.5.)

c. Would a 99% confidence interval be narrower or wider than the interval computed in Part (b)?
Justify your answer.