Across how many centers was the study conducted?

• A. 1 center
• B. 4 centers
• C. 2 centers
• D. 3 centers

Answer: (D)

The main idea here is why a study is done across more than one site. Using multiple centers helps ensure that the findings aren’t tied to the habits, equipment, or patient population of a single place. With three centers, you get enough variation in practice settings to show that the results are likely to hold in different clinics, which boosts generalizability and reduces center-specific bias. It also keeps the study feasible: more centers can improve generalizability, but too many add logistical complexity and potential variability that make analysis harder. A single center risks results that only reflect that one location; too few centers may miss important differences in how the intervention performs in other settings. Three centers strike a balance, capturing meaningful variation while remaining manageable, which is why this design is often chosen for broader applicability.