Which of the following is considered a direct identifier in research?

A direct identifier is any piece of information that can be used to uniquely identify an individual. An email address is a prime example of a direct identifier because it can be directly traced back to a specific person, enabling researchers to contact or identify them individually. In research contexts, protecting direct identifiers is crucial to maintain confidentiality and ensure the privacy of participants.

Other options, while containing valuable information, do not uniquely identify individuals on their own. Age and gender are demographic characteristics that, when combined with other data, could lead to identification but are not direct identifiers by themselves. Similarly, survey responses may reveal insights but do not provide a clear link to an individual unless paired with other identifiable information.