Answer:
An observational study
Explanation:
observational studies are those a study where the researcher observes the effect of a defy factor, diagnostic test, treatment or other intervention without trying to change who is or isn't exposed to it. Cohort study and control studies are of two observational studies. These are the part of fundamental of epidemiological research. These are called observational studies because the investigators observe individuals without manipulation and intervention. These studies are an important category of study design. Well, design observational studies maybe the next best method to address these types of questions.