Calculate sales lift, adjusting for any differences between the test and control group. Post navigation Which of the following factors is required to establish causality? In an advertising experiment using before-after design, 3000 customers are randomly assigned to 3 groups. All groups are exposed to the existing advertisement for round 1 of the experiment. In round 2, new advertisements are shown to groups 2 and 3, while group 1 continues to see the old ads.