Floating around the internet today is the stat that 61% of world series game 1 winners go on to win the world series. (Interestingly, 84% of the last 13 have gone on to win it, but I'm not looking at that fact right now.)

I was curious what the probability of this happening is, if I assumed a simple model where each game in the best of 7 series is a fair coin flip. I expected that the probability would be much lower than 61%. Why? Because I assumed that the psychological advantage combined with whatever skill advantage is implied by the team having won the first game would lead to a much higher chance of those first winners (the Giants, this year) winning the whole thing.

But, I was surprised to find that the probability is 0.66.