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4. A well-evaluated cognitive behavioral program is administered to youth on juvenile probation to teach them how to reduce levels of aggression. Researchers are interested only in whether or not the youth improved (i.e., if their aggression was reduced) and have good reason to believe that the individual's aggression will decrease because research has found it to be effective. Therefore, use a one-tailed t test to identify whether or not levels of aggression (high numbers reflect greater aggressiveness) were reduced after the cognitive behavioral program. Before and after results are presented below: Aggression Probationers Before (X1) After (X2) 18 15 15 13 14 14 16 14 10 7 17 14 14 11 15 14 10 11 9 16 12 13 13 9 7 16 15 12 14 Test the null hypothesis that the cognitive-behavioral program has no effect on level of aggression. (Use a = .05; follow the 8 steps). (30%)