A sensory psychologist wants to determine if a sensory threshold differs depending on which nostril is used. He obtains 30 introductory psychology student volunteers and measures the absolute threshold, in parts per million, for detecting the scent of peppermint. Participants are randomly assigned to three equalsize groups: (1) Scent administered to the left nostril, (2) Scent administered to the right nostril, and (3) Scent administered to both nostrils. Each participant is tested individually by an experimenter who does not know what the hypothesis is and does not know which nostril is being used.