Rosemary Stein, a former Vice President here at Marden-Kane, explains why an affidavit is necessary in a sweepstakes. An affidavit is a legal statement made in writing. Sweepstakes sponsors use this document to determine your eligibility to win a prize. The winner signing the affidavit declares the facts stated in the affidavit to be true, and confirms this under oath. The affidavit will ask you to confirm that: 1)