Some people think that playing video games is related to aggressive behavior.  If you were to conduct a study examining these variables, you would need to give operational definitions for them. Please give an operational definition for the variable “aggression” as a dependent variable:

Research is a process of systematic investigation using a set of detailed and methodic tools to help build knowledge, and theory about a particular area. The process involves starting with a research question, forming a hypothesis, and building the research methodology and design, in order to seek the research question. 
The research would involve the use of variables that are defined factors whose values can be changed. Variables are the core of research, whether it be quantitative or qualitative research.

Research begins with the hypothesis stating the relationship between the two variables that will be established by the study. Variables are of two kinds: independent variables and dependable variables. The independent variable (IV) is the factor that is a constant component in the study or experiment and is manipulated by the researcher, while the dependent variable is the factor that depends on the IV and would change values.