In a comparison study, which conclusion cannot be drawn if donepezil is tested only against combination therapy?

• A. The combination therapy is less effective than no treatment.
• B. Donepezil shows better results than memantine alone.
• C. Both treatments have equal efficacy in improving outcomes.
• D. The study confirms the superiority of donepezil over placebo.

Answer: (B)

When evaluating the conclusions drawn from a study that tests donepezil exclusively against combination therapy, it's important to understand the implications of such a design.

Testing donepezil against combination therapy does not allow for a direct comparison with memantine alone. This means that any conclusion about donepezil's relative effectiveness to memantine by itself cannot be accurately made since the study doesn't include that variable in its design. Therefore, you cannot conclude that donepezil shows better results than memantine alone simply based on this study, as it lacks the necessary control group for memantine.

In contrast, conclusions can be made about the combination therapy in relation to donepezil. For instance, the study could indicate that the combination therapy is either more or less effective than no treatment, but it won’t provide a meaningful insight into how donepezil compares specifically with memantine alone. Thus, the conclusion that memantine alone shows specific outcomes compared to donepezil cannot be established.