With quota sampling a researcher stands at a street corner and conducts interviews until obtaining a quota representing the relative sizes of various groups in the population. For instance, the quota might be 50 factory workers, 100 housewives, 60 elderly people, and 30 blacks. Is this a probability or nonprobability sampling method? Explain, and discuss potential advantages or disadvantages of this method. (Professional pollsters such as Gallup used this method until 1948, when they incorrectly predicted that Dewey would defeat Truman in a landslide in the presidential election.)