The aim of experimental research is to ascertain the causality of two different variables, that is to say, to ascertain whether the changes of one variable is caused by the changes of another one. Experimental research usually have two main features: 1. Researcher need to change one variable(independent variable) in order to observe the changes in another one(dependent variable). 2. The same time changing the independent variables, researchers should also control the irrelevant variables, making sure they won't affect the result of the experiment.

Beside experimental research, there exists a kind of research between experimental research and non-experimental research, which is called quasi-experimental research. The control of irrelevant variables in this kind of research is superior to non-experimental research, but not as strict as that in experimental research. We may not keep the irrelevant variables all equal in control groups in experimental researches, so we may have to compromise, using quasi-experimental research to obtain useful information.

The last kind of research is non-experimental research, whose control of irrelevant variables is way less stricter, and it is usually used for originally existed relationships between variables. Fewer factors could be controlled in non-experimental research, and it doesn't include control groups for comparation, in contrast to quasi-experimental research.