a. This study is observational as the researchers observed the behaviors of the participants without intervention. b. The independent variable is the aggressive behaviors of the participants at early ages. c. The dependent variable is the occurrence of unemployment of these participants at a later time. d. The end outcome of unemployment may be a result of numerous confounding factors besides aggressive behaviors at early ages, these may include family issues (lost of parents), health issues, education methods, etc. e. The three groups of subjects in the study are participants who tend to (1) hurt other children, (2)kick objects when angry, or (3)attacking others without reason, among 300 participants at ages 8, 14, 27, and 36.