How are the battleground state probabilities calculated?
The polls for a state are collected over the previous 1-2 weeks and the election within that state is simulated 50,000 times from those polls. Then the number of times the candidate wins the election in those simulations is divided by 50,000 and the probability is reported. (Technical note: What is taking place here is we are treating the polls as multinomial distributions and using WinBugs to sample from the posterior distribution.
