What evidence do I need to prove that my parents are financially dependent on me?

I understand that to include parents in my CBI application for Antigua and Barbuda, I need to prove that they are financially dependent on me. What kind of documents should I provide to establish this?

Answers

On Robert Wilkinson answered:

This is normally done by way of a signed affidavit. Bear in mind that they must also be living with the main applicant as well as being financially supported by them.