How much is a win worth in the MLB

There is much talk about a baseball players wins probability added (WPA) and similar stats. I wanted to take a step back and see how much is adding X number of wins to a team actually worth in terms of a) reaching the playoffs and b)winning in the playoffs.




I looked at each team’s W-L record for the last five seasons (2005-2009) and calculated the effect of adding or subtracting wins to their record in terms of reaching the playoffs.



So if a team was 4 games behind the wildcard team adding 1,2 or 3 games has no effect, and the probability of making the playoffs stays at 0. Adding 4 games would lead to a playoff so the chances of making the playoffs is considered to be 50%. Adding 5 or more games leads to a 100% chance of making the playoffs.



Doing this for all 150 teams-seasons showed that each win increases a team’s chances of making the playoffs by 2.8% the actual line is a sigmoid but it is very linear except at the extremes.

However when we get to the playoffs the situation is quite different. I looked at seven years 2002-2008 where there were 49 playoff series. In three of these both teams had the same regular season record. In the other 46 the team with the best regular season record went 24-22 which is little better than a coin toss.

Even splitting the 46 into the 24 with the smallest regular season record difference (5 games or less) and the 22 with the biggest difference(6 or more games) had no effect with the 22 biggest difference teams only going 12-10, the small difference teams went 12-12.



So maybe Billy Beane shouldn't have been too upset when he complained that his "S*** doesn’t work in the playoffs."