- The independent variable: the phenomenon or situation that is manipulated by the researcher
- The dependent variable: the behavior or effect that is measured by the research as a result of the manipulation
- The moderator variable: the factor which is ‘measured, manipulated or selected’ by the researcher to determine whether or not it changes the relationship between the independent variable and the dependent variable.
- The control variable: a potential the independent variable that is artificially held constant by the researcher throughout the experiment (Burns, 2000).