From FiveThirtyEight:

Right now, our trusty little model of Massachusetts gives Martha Coakley just a 25 percent chance of prevailing tomorrow. Intrade also puts her odds at about 1 in 4. My subjective assessment might be a little better than that, but not much.

People are acting, however, as though 25 percent is the same as zero percent. And — as disappointing as it might be to be in this position — obviously it is not. This is not some basketball game where the score suddenly became Brown 75, Coakley 25; a 25 percent chance of winning means, quite literally, 25 percent.