Final answer:
The main benefit of naturalistic observation studies is that they provide honest and valid data by observing subjects in their natural environments, which can be generalized to real-life settings.
Step-by-step explanation:
The benefit of naturalistic observation studies is the honesty of the data that is collected in a realistic setting. Naturalistic observation studies provide validity because participants behave as they would normally, enhancing ecological validity and allowing for greater generalization of results to real-life contexts. However, while providing the opportunity for the collection of valid, true-to-life information from realistic situations, these studies are characterized by a lack of control over environmental variables, making them difficult to set up and control.
It is important to note that naturalistic observation does not typically permit researchers to establish cause-and-effect relationships because of the inability to control variables and the observational nature of the research. Therefore, answer 'd' is incorrect as cause and effect determination is not a benefit of this approach.