In a single-blind study, who does not know their group assignment?

In a single-blind study, the design specifically keeps the participants unaware of which group they belong to, whether it be the treatment or control group. This lack of knowledge helps to reduce bias in participant responses and behaviors, as they cannot influence their reactions based on what they think they are receiving. Meanwhile, the researchers are aware of the group assignments and can conduct the study and analyze the data without that information being obscured.

This design contrasts with a double-blind study, where both participants and researchers are unaware of the group assignments. In the context of the options provided, only the participants being unaware aligns with the definition of a single-blind study, making this the correct choice. Understanding this distinction is crucial in experimental research design, as it influences the validity and reliability of the outcomes being assessed.