In studying the effectiveness of monetary rewards on seat belt usage, a firm has been giving out lottery tickets to employees wearing their belts when entering the company parking area. At the end of each week, the holder of the winning ticket gets a free dinner at a local restaurant. Before the experiment, only 36% of employees wore seat belts. After 1 month of the lottery, the usage rate is up to 57%. 

a. Identify the dependent and independent variables in this experiment.
b. Is a control group involved in this experiment? If so, who?