Answer: Systematic random sampling technique
Explanation:
A systematic random sampling technique is a kind of random sampling method in which a researcher samples participants from a large population by fixing a random beginning point and a fixed periodic interval to select them.
Given : A researcher selects every 12th person admitted to the emergency department with a closed head injury for a research study.
i.e. there is a fixed interval of selection person.
Hence, the this is known as systematic random sampling technique .