Mutual funds. In Exercise 31 of Chapter 2, you took an SRS of funds from a mutual fund company. Most companies have mutual funds in a number of different categories, for example, domestic stock funds, foreign stock funds, and bond funds, and the returns in these categories differ.
a Divide the funds from the company into strata. You may use categories provided by the fund company, or other categories such as market capitalization. Create a table of the strata, with the number of mutual funds in each stratum.
b Using proportional allocation, take a stratified random sample of size 25 from your population.
c Find the mean and a 95% CI for the mean of the variable you studied in Exercise 31 of Chapter 2. How does your estimate from the stratified sample compare with the estimate from the SRS you found earlier?