Volatility in Baseball Probabilities

Let me pose a question that address in further as this blog progresses: What is the appropriate level of volatility in an efficient forecast? Here is the forecast of the World Series winner for the three most probable teams: Phillies, Yankees, and Red Sox, based on BetFair prices. The probabilities cover the first week and a half of the season. Useful volatility represents new and meaningful information, un-useful volatility is just random movement. While the starting pitching has been a little less than amazing, the Phillies (7-2) are basically achieving at expectation and their probability remains essentially flat. Having to make the playoffs and then win three rounds, it is essentially impossible for them to move much beyond 25% this early in the season, even if they win every game. The Yankees (5-4), just dropped 2 of 3 from the Red Sox (2-7), but remain slightly up and the Red Sox slightly down from the start of the season. Does it seem reasonable that the Red Sex have a 13% of winning the World Series? Does going 0-6 in a 162 game season mean they are 25% less likely to win or does it provide minimal new information? The Yankees are clearly moving upward in because of the probability of making the playoffs the AL East winner increases their chances of doing well in the playoffs, but is that putting too much weight on the first step? These are questions I will address in later posts …