A supervisor at ABC Agency wants to know whether the type of incentive system offered to customer service agents will affect the customer service ratings the agents receive. She randomly assigns half of the customer service team to a group that will be rewarded based on the agency's normal incentive system and the other half to a group that will be rewarded based on a new incentive system. She compares the average customer service rating of the normal incentive system group and the new incentive system group at the beginning of the experiment and at the end of the 6-month monitoring period. In this experiment, the dependent variable is _____________