There's an interesting article on negative probabilities by Gábor Székely in which he shows that they can be generate by flipping a "half coin" -- a coin that,

There's an interesting article on negative probabilities by Gábor Székely in which he shows that they can be generate by flipping a "half coin" -- a coin that, if flipped twice, gives the result from a single flip of an ordinary coin. http://wilmott.com/pdfs/100609_gjs.pdf http://wilmott.com/pdfs/100609_gjs.pdf