Wednesday, November 19, 2008
Updated: December 11, 1:00 PM ET
Playoff Odds: How it works
By John Hollinger
Yep, it's back.
It's once again time to unveil the Hollinger Playoff Odds.
The idea is to predict what a team's odds are of making the playoffs, winning the division, making the Finals, etc., by simulating all the remaining games in the NBA season. We have a computer at ESPN headquarters in Bristol, Conn., that automatically plays out the rest of the season every night -- not once, but 5,000 times. And we can see from those 5,000 trials how many times a certain outcome resulted, then assign a probability from it. For example, if the Blazers make the playoffs in 2,500 of our trials, we say their odds of making the playoffs are 2,500 divided by 5,000, or 50 percent.
This tool doesn't just play out the regular season, though -- it plays out the postseason with seedings and even runs the draft lottery. As a result, we can get an idea of the probability of all sorts of outcomes; the most prominent is the team's median record from the 5,000 trials. As a reminder, this tool is completely, 100 percent automated, so my obvious, long-standing bias against your favorite team is not a factor here.
As always, the output of a product is only as good as its input, so let's explain a little about how this is derived. The computer starts with the day's Hollinger Power Rankings. Then, in each of the 5,000 times it replays the season, it makes a random adjustment up or down to allow for the possibility that a team will play better or worse than it has done thus far. (I call this the Anti-Dennis Green Postulate; i.e., maybe they aren't who we thought they were.)
Additionally, the results regress to the mean. This is more important early in the season, and what it essentially means is that even though a team might start 10-0, it's not necessarily bound to go 82-0. The effect of this will reduce sharply after the first quarter of the season or so, but in the early going of most seasons, it's necessary to prevent us from projecting 77-win seasons and the like.