Final answer:
Epidemiological studies often use the observational study approach to measure characteristics in a sample without manipulating variables, which is especially useful when experiments are not possible.
Step-by-step explanation:
True, epidemiological studies observe people as they behave in their normal environment rather than under controlled or experimental conditions. An observational study measures characteristics in a sample without attempting to manipulate the variables of interest. The naturalistic observation approach allows for observing behavior in its natural context, which can provide a wealth of information about real-world behaviors and conditions. This method is particularly beneficial when experimental studies are not feasible, practical, or ethical, such as studying the effects of smoking on health.