Final answer:
The key difference between the experimental method and naturalistic observation is that the experimental method uses control groups, while naturalistic observation does not.
Step-by-step explanation:
The key difference between the experimental method and naturalistic observation is that the experimental method uses control groups, while naturalistic observation does not. In an experimental method, researchers manipulate variables and compare the results between the experimental group and the control group. On the other hand, naturalistic observation involves observing behavior in its natural context without any manipulation of variables.