Under what circumstances would a field experiment be most useful?

Question

Quizplus · Accepted Answer

A field experiment would be most useful when strict random assignment cannot be used for ethical reasons. For example, if the researcher wants to study the effects of smoking on lung cancer, it would be unethical to randomly assign participants to a smoking group. Instead, the researcher can conduct a field experiment in which they observe and measure the health outcomes of individuals who choose to smoke versus those who do not.

Under What Circumstances Would a Field Experiment Be Most Useful