Question

the difference between an observational study and an experiment is that
in an observational study, only one group is studied, and in an experiment, two groups are studied.
in an observational study, the researchers do not control treatment, and in an experiment, they do.
in an experiment, cause - and - effect is analyzed, and in an observational study, it is not.
in an experiment, one group is studied over a short period of time, and in an observational study, the group is studied over a longer period of time.

Explanation:

To determine the correct answer, we analyze each option:

• Option 1: Both observational studies and experiments can involve one or more groups, so this is incorrect.
• Option 2: In an observational study, researchers observe without controlling treatments. In an experiment, they manipulate (control) treatments to study effects. This accurately describes the key difference.
• Option 3: Observational studies can also analyze cause - effect (though with more limitations), so this is wrong.
• Option 4: The duration of study is not the defining difference between an observational study and an experiment.

Answer:

B. in an observational study, the researchers do not control treatment, and in an experiment, they do.