There are generally three methods: 1. Control methods of some measured variables and temporary measured variables: Measured variables refer to the persistent characteristics of different degrees among subjects under the same external conditions. Such as age, gender, nationality, culture and other relatively stable individual differences; Temporary subject variables refer to the discontinuous functional state of subjects, such as fatigue, excitement level, incentives, etc. Generally, the following methods are used to control this irrelevant variable, including instruction language control, standardizing the attitude of the subjects to the subjects, double-blind experiments, and controlling the individual differences between the subjects and the experimental group and the control group. 2. Control methods of environmental variables and some measured variables: mainly refer to non-independent environmental factors, irrelevant variation factors generated in the process of experiment implementation, some measured variables or temporary measured variables. There are mainly the following control methods: (1) operation control method, which mainly refers to the specific operation of the subject and excludes the influence of some variation factors on the studied problem. It has two aspects, namely, excluding irrelevant variables and keeping them unchanged; (2) Design control method, that is, controlling the effects of irrelevant variables that may be mixed in the experimental results through experimental design, including the balance of irrelevant variables (dividing subjects into two groups with equal irrelevant variables: control group and experimental group), the cancellation of irrelevant variables (making each subject in this group receive two or more experimental treatments respectively, including complete internal design and incomplete internal design), randomization method and pairing method. (3) Statistical control methods, including incorporating irrelevant variables and statistical control.