A UX Designer is evaluating whether to perform a moderated or unmoderated usability study on...

The distinguishing advantage of a moderated usability study is the researcher's ability to interact with participants and investigate observations in real time. Therefore, A is correct, which matches the uploaded study guide answer. During a moderated session, the researcher observes a participant completing defined tasks while remaining available to ask neutral follow-up questions. For example, if the participant hesitates, misunderstands a label, or abandons a workflow, the moderator can investigate the underlying reason without simply relying on analytics or a post-session questionnaire. This enables collection of richer qualitative evidence regarding the participant's reasoning and mental model. Options B and C describe typical advantages of unmoderated research. Because no researcher needs to attend each session, participants can usually complete studies asynchronously from different locations. That model generally scales more easily and can reduce both cost and researcher time. The tradeoff is depth versus scalability. Moderated testing provides deeper contextual information and allows probing, whereas unmoderated testing provides broader reach and scheduling flexibility. Because the scenario specifically asks what would justify choosing the moderated approach, the capability to ask follow-up questions when usability issues appear is the decisive criterion.

Study Guide reference/topics: Moderated testing, unmoderated testing, qualitative research, follow-up questioning, usability study design.

==================================