Independent variables can be divided into continuous variables and category variables. If the independent variable manipulated by the experimenter is a continuous variable, the experiment is a functional experiment. If the independent variable manipulated by the experimenter is a category variable, the experiment is a factor type.
In psychological experiments, independent variables are variables manipulated and mastered by experimenters.
In mathematics, y=f(x). In this equation, the independent variable is X and the dependent variable is Y. When this equation is applied to psychological research, the independent variable refers to the factors or conditions that cause the dependent variable to change, so the independent variable is regarded as the cause of the dependent variable.