Researchers tested whether a new drug called Alzapen (DRUG) could shrink brain plaques that lead to Alzheimer's. Four hundred patients were recruited from a large university hospital; half were given the new drug while the other half were given a placebo. The results indicated a statistically significant reduction in plaque size (PLAQ) for patients taking the new drug as opposed to patients taking the placebo. Coding for study variables: DRUG1 = Alzapen drug; 2 = placebo PLAQplaque size; 0-700 m2 What study design was used in this scenario