Much like the update last month, nothing in how we calculate our playoff odds has changed, but we’ve added a new feature to the page. We are now reporting the distribution of wins from the Monte Carlo simulation.
- The 25th percentile;
- The 75th percentile; and
- A histogram of projected wins.*
*The average is already reported as expected wins.
You can find this if you select the new display option in the dropdown of the same name.
During this winter’s iteration of the interminable debate about WAR, there was some discussion about reporting uncertainty in stats. Hopefully, providing these graphs of our playoff-odds output will help readers understand the playoff odds as something larger than a mere median estimate. It should be noted that we aren’t formally estimating error, just reporting the distribution of wins that have always been underlying the projections we show on the page. We don’t currently have error estimates for the projection systems that feed into the playoff odds.
The distribution is just the frequency of total win outcomes for a team’s 10,000 simulated seasons. The graph is scaled to be used within the same playoff-odds page, in order to compare a team’s range of outcomes to other teams. It shouldn’t be used to compare changes over different days or projection mode, because the differences in axes could make for a misleading comparison. For the curious, I’ve taken distributions from different days and projection modes and properly scaled the axes to demonstrate how they look in comparison to each other.
The Braves started 2018 with 72.9 projected wins and have improved that projection to 80.4 wins (entering May 9th). So the distribution has shifted to the right. I’ve also plotted the coin-flip distribution. It’s much like the the two FanGraphs projection distributions, except it will be shifted towards 81 wins. The season-to-date projection mode has a flatter distribution, because that projection mode adds random error terms to team’s game win probability.
As usual, please let us know if you have any problems or find any bugs.
I code a bunch of things here. I really need to update my blog about statistics at stats.seandolinar.com.