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LucyLu
12-03-2015, 06:56 PM
Hi there,
I have this assignment question pertaining to confidence intervals and I have to admit that I am a little lost in this class and I have no idea where to get started. If someone could give me an idea of how to solve it or guide me through it, that would be great. Thanks!


A Phoenix Wealth Management/Harris Interactive survey of 1,500 individuals with net worth of $1 million or more provided a variety of statistics on wealthy people (Business Week, September 22, 2003). The previous three-year period had been bad for the stock market, which motivated some of the questions asked.

a. The survey reported that 53% of the respondents lost 25% or more of their portfolio value over the past three years. Develop a 95% confidence interval for the proportion of wealth people who lost 25% or more of their portfolio value over the past three years.
b. The survey reported that 31% of the respondents feel they have to save more for retirement to make up for what they lost. Develop a 95% confidence interval for the population proportion.
c. Five percent of the respondents gave $25,000 or more to charity over the previous year. Develop a 95% confidence interval for the proportion who gave $25,000 or more to charity.
d. Compare the margin of error for the interval estimates in parts (a), (b), and (c). How is the margin of error related to ? When the same sample is being used to estimate a variety of proportions, which of the proportions should be used to choose the planning value p? Why do you think p = .50 is often used in these cases?