Make two batches of cookies, one with bleached flour and one with unbleached flour; twenty tasters try both types and rank which type they like best.

Make two batches of cookies, one with bleached flour and one with unbleached flour; twenty tasters try both types without knowing which ones they are eating and rank which type they like best.

Make two batches of cookies, both with bleached flour; one taster tries both types and ranks which type they like best.

Make two batches of cookies, one with bleached flour and one with unbleached flour; one taster tries both types and ranks which type they like best.