Answer:
Natural experiment
Explanation:
Natural experiment is the study of empirical, which comprise of the individuals who are exposed to the control as well as the conditions of the experimental , which are determined or evaluated by the nature or through other kinds of factors that are outside the person control.
The procedure of governing the exposures resemble the random experiment. This experiment are not controllable and are the observational studies. So, the event is naturally occurring, then it is an example of the natural experiment.