Give a variable that could be used to stratify the population for each of the following studies. List at least four subcategories for each variable.
a. A political party wants to conduct a poll prior to an election for the office of U.S. senator in Minnesota.
b. A soft drink company wants to take a sample of soft drink purchases in an effort to estimate market share.
c. A retail outlet wants to interview customers over a one-week period.
d. An eyeglasses manufacturer and retailer wants to determine the demand for prescription eyeglasses in its marketing region.