While mathematically correct, this does not seem to be how people use with that phrase. "X is probably going to happen" implies there is some evidence in favor

While mathematically correct, this does not seem to be how people use with that phrase. "X is probably going to happen" implies there is some evidence in favor of X, while "X is probably not going to happen" implies evidence against. Now, in regular speech, people do not feel compelled to force themselves to choose one or the other, but are just as likely to say "I have no idea", implying no evidence in either direction. From an Information Theory point of view, 50% probability means zero information, and 25%/75% probabilities mean one bit of information against/in-favor-of the event. This sounds roughly consistent with the results of the poll, with people assigning higher probabilities implying higher information density of the evidence.