A report in Newsweek about the relationship among diet, genes, and disease (Underwood and Adler, 2005) discussed the E4 allele for a protein known as Apo E and said "an estimated 15 to 30 percent of the population has at least one copy of the allele." People who have the allele are at higher risk for diabetes, heart disease in smokers, and Alzheimer's disease.

a. What is the population parameter of interest in the quote?

b. Would it make more sense to find a confidence interval for the population parameter you described in part (a) or to conduct a hypothesis test for a specific null value for it? Explain. If your answer is "a hypothesis test," specify the null value that you would test.

c. The phrase "an estimated 15 to 30 percent" indicates that scientists don't know precisely what percentage of the population has the allele. Explain why they don't know.