Charity events often use silent auctions. A donated item, such as a date with a movie star, is put up for bid. (See www.ecorazzi.com/2008/02/22/ebay-and-oxfam-help-you-win-a-date-with-colin-firth for a description of auctions for celebrity dates with Colin Firth and Scarlett Johansson.) In a silent auction, bidders write down bids and submit them. Some silent auctions use secret bids, which are submitted in sealed envelopes and kept confidential. Other silent auctions are open: the bidder writes down a bid on a bulletin board that everyone present can see. Which kind of auction would you expect to raise more revenue for the charity?