Answer:
The best answer to the question: Chris has used a (n) _______ design for his study, would be: Interventional Clinical Trial design.
Step-by-step explanation:
The reason for why the answer would be a clinical trial, instead of the closest other option, which would be a Cohort Study, is the fact that what is being evaluated here is the effectiveness of a new treatment program against substance abuse issues. The Cohort Study does not test for an actual treatment, but rather, the situational characteristics that surround the groups being observed and the measures that could be taken to prevent certain outcomes. In clinical trials, however, the focus is precisely to test the outcomes brought on by a new medication, or any other form of treatments, and it requires both a test group, and a control group to determine the outcomes. Since Chris wants to see the success of the treatment on this group of substance abusers, and uses as control, a group who displays the same characteristics, but did not become a part of the tested group, this is known as an Interventional Clinical Trial.