creates 3 different training classes, one using all positive rewards, the second using all positive punishments, and the third using both rewards and punishments. There are about 200 undergraduate students with dogs. Doug asks 90 students to try his classes. The students then rate the training on a scale of effective to ineffective and next by level of liking from 0% to 100% liking. The highest rated training was for the mix of rewards and punishments. Identify each of the following for Doug's Dog training study: a) Population b) Sample c) Independent variable(s) d) Levels of the independent variable E. Dependent variable