Whenever we send Cumulus coupons, we deliberately leave out a small group of customers. This group is selected at random and changes with each offer. This method (control groups) enables us to measure customer acceptance and the impact of our offers. We can then use these findings for future activities. The goal is to align our offers with our customers' needs. This means that the customers in the control group can't benefit from offers in individual campaigns, although all customers are treated equally in the long term because everyone is included in the control group at some time or another.