Statistical regularity : The inherent regularity exhibited by a large number of repeated experiments or observations.
Random phenomenon : In individual experiments, the results show uncertainty, and in a large number of repeated experiments, the results have statistical regularity.
Experiment : The observation of a certain characteristic of something is an experiment. Observations of different characteristics of the same thing are different experiments.
A randomized trial with 3 characteristics:
1, can be repeated under the same conditions
2. There is more than one result of each experiment, and all possible results of the experiment can be specified in advance
3. Not sure which result will appear before conducting an experiment