282, 284-285 10.3. Why Experiments Support Causal Claims Fill in the blanks to complete the passage about an example of a researcher who is establishing groups in an experiment. Dr. Keller wants to test the effect of a new antianxiety medication. He recruits a group of anxious patients and randomly assigns them to two groups. The first group will receive his new medication and the second group will receive a sugar pill. The first group is called a -. The second group is called a -. Dr. Keller makes sure that length of treatment is a - by treating both groups for the same length of time. control groupplacebo groupconfoundtreatment groupcontrol variable