The definition of natural experiment?

Quasi-natural experiment is a method of social science research. Compared with the real experimental research, it adopts a certain control program and flexibly controls the experimental objects by using natural scenes. Including the control group without pre-test design and the peer-free control group design. Different from the real experimental design, the experimental subjects are not randomly assigned to the experimental group and the control group, so the rigor is slightly lower, so the validity of the causal conclusion is lower than that of the real experimental study, but the advantage is that the required conditions are flexible, and it has wide applicability when all irrelevant variables that may affect the experimental results are uncontrollable.

Natural experiment refers to an experimental research method that subjects (groups) are exposed to experimental or controlled conditions naturally or through other non-observer control factors. The division of experimental group and control group is similar to random experiment.