Answer:
This procedure is know as:
D. known-groups paradigm.
Step-by-step explanation:
Dr. Sheffield already knows the traits of each of the two groups - the gamblers and the alcoholics. What he is doing is establishing the validity of his measure by applying it to a group that has a certain trait - the gamblers - and to a group that does not have a certain trait - the alcoholics. This procedure is an example of known-groups paradigm. It is important to note that this type of procedure can also be applied to two groups that do possess the same trait, but with the purpose to verify which one will score higher on it.