A survey by the AARP (Money, June 2007) reported that approximately 70% of people in the 50 to 64 age bracket have tried some type of alternative therapy (for instance, acupuncture or the use of nutrition supplements). Assume this survey was based on a sample of 400 people.

a. Identify the relevant parameter of interest for these qualitative data and compute its point estimate as well as the margin of error with 90% confidence.

b. You decide to redo the analysis with the margin of error reduced to 2%. How large a sample do you need to draw? State your assumptions in computing the required sample size.