I received the following email the other day:

I read the abstract for your paper What is the probability your vote will make a difference? with Nate Silver, Aaron Edlin [to appear in Economic Inquiry]. I’d note that the abstract prima facie contains an error. Your sentence in the abstract, “On average, a voter in America had a 1 in 60 million chance of being decisive in the presidential election.” can not be correct. If we assume that this sentence is correct that means that given the actual turnout of 132,618,580 people the sum total probability of voters being decisive is larger than one. This of course [sic] is impossible. The total amount of decisiveness must be at most one (although obviously the sum total can be lower than one if the voters are not equally disposed to both candidates). . . .

The above argument is at first appealing but is not actually correct. Actually the total probability can exceed 1. For a simple mathematical example, see p.425 of this paper. The reason the total probability can exceed 1 is that it is possible for many voters to be decisive at the same time.