What are the confidentiality issues with PIDs?

PIDs should be kept private by the recipient. A PID is not just a password. Each PID is unique and identifies the feedback provided by a specific Responder for a specific Subject.

PIDs should never be "loaned" to anyone else. If the wrong person uses a PID, their response will not be credited to them. 

For security reasons, restrict access to PID information to prevent anyone from impersonating a Responder. Ask Responders to keep their PIDs confidential. Warn them that if they share their PID with someone else, their responses may not be tabulated, while the other person’s responses may be counted instead.