Experimental and nonexperimental research are distinguished by the degree of control that the researcher has over the subjects and conditions in the study.

You must distinguish between manipulation and assignment versus observation.

An experiment is an investigation in which at least one variable is manipulated by the researcher.

You have to know what a variable is:

• A variable is an aspect of the testing condition that can change or take on different characteristics with changes in conditions.

Learn This:
You have to know the difference between an independent variable (IV) and dependent variable (DV).