A manager at ABC agency wants to know whether the type of sales tactics used by her sales team members will affect the volume of sales generated. She randomly assigns half of the sales team to use the agency's normal sales tactics and the other half to use a new tactic involving high pressure and limited time promotions. She compares the average sales volume of the normal tactic group and the new tactic group at the beginning of the experiment and at the end of the 6-month sales period. In this experiment, the independent variable is _____________