New User Design includes which group?

• A. Initiators only
• B. Prevalent users
• C. Random sample of all users
• D. Non-users

Answer: (A)

The main idea being tested here is focusing on people at the moment they start a treatment, rather than those who are already using it or never started. A new-user design defines the start of follow-up at initiation and only includes individuals who begin the therapy during the study period. This approach avoids biases that come from including people who were already on the treatment (prevalent users), whose duration of use and past exposure can distort effect estimates, and from including non-users, who don’t help answer questions about starting treatment.

So the best choice is initiators only because it captures the immediate effects and characteristics at the moment of starting therapy, ensuring a clear, well-defined exposure from the outset. Including prevalent users or non-users would dilute or bias the comparison, and taking a random sample of all users would mix incident and prevalent users, undermining the design’s purpose.