## Tuesday, April 13, 2010

### Playoff Probabilities

In order to get a sense of each team's chances, I decided to run a couple simulations of the first round.

For the first set of simulations, I calculated each team's winning percentage on the basis of pythagorean expectation after correcting for schedule difficulty, empty netters and shootout goals. In the charts displayed down below, the probabilities determined on this basis can be found in top half of each individual chart (next to the cell titled 'PYTHAGOREAN').

In the second set of simulations, the methodology was somewhat more complicated. Without getting too specific, I computed each team's theoretical winning percentage on the basis of the following inputs:
• Each team's corsi ratio with the score tied during the regular season (as a determinant of shots for and against at EV)
• The career EV save percentage of each team's starting goalie (as a determinant of each team's EV save percentage and the shooting percentage of its opponent). Each goalie's career save percentage was regressed to the league average based on the number of career EV shots faced to date (for goalies facing fewer shots, the regression was stronger; for goalies facing more shots, the regression was weaker)
• Each team's tendency to draw and surrender powerplays during the regular season (as a determinant of time spent on the powerplay and penalty kill)
• Each team's shot rate on the powerplay and shot rate against on the penalty kill during the regular season (as a determinant of powerplay goals for and against)
The probabilities associated with these inputs can be found in the bottom half of each individual chart (next to the cell titled 'UNDERLYING #'s').

For each set of simulations, I simulated the first round 10 000 times. Home advantage was taken into account for both sets of simulations. The results are displayed below, with the Eastern Conference following the West.

The row next to each of the four numbers shows each team's probability of winning the series in that many games. The highlighted row shows each team's chance of winning the series.

By way of example, consider the San Jose Colorado series. If each team's winning percentage is computed on the basis of pythagorean expectation, the Sharks have a 11.3% chance of winning the series in a sweep and a 68.5% of winning the series.

If, on the other hand, the second method is applied, the Sharks have a 15.5% of winning in a sweep and a 77.9% chance of winning overall.

Overall, the two methods yield comparable results, except in the case of the DET-PHX and BUF-BOS matchups. The first method suggests that the Coyotes should win slightly over half the time, whereas the second indicates that the Wings are the clear favorite.

The discrepancy is even greater for the Sabres and Bruins matchup. According to the PYTHAGOREAN method, the Sabres should win some two-thirds of the time, yet the second method produces the opposite result.

Scott Reynolds said...

This is great! Just out of curiosity, is Boston the top team in the East going by the more complicated method. When I was looking at their out-shooting results I was surprised at how good they were.

Sunny Mehta said...
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Sunny Mehta said...

Interestingly, the bookies agree with the underlying #s for the Detroit series but not for the Boston series.

Sunny Mehta said...

This is awesome work, JLikens.

JLikens said...

Scott:

Boston is, in fact, the best team in the East by the underlying numbers method. I'll make a post showing each team's expected winning percentage according to each method.

Sunny:

That's interesting. I suspect a lot of that has to do with Detroit's reputation and the fact that they cleaned up down the stretch.

It may also reflect some wariness of Phoenix on the part of the odds makers.

Scott Reynolds said...

Interesting stuff with respect to Boston. It's kind of fun (though not for Bruins' fans) to see a team go from way overrated riding hot shooting to way underrated when the shooting percentages completely collapse. They're actually a better territorial team this year than they were last.

sNaFu said...

the major flaw of this analysis is that you're basing it off regular season statistics that often correlate poorly with playoff results. If the regular season stats were a worthy indicator then neither MTL or PHI would be where they are now

JLikens said...

"the major flaw of this analysis is that you're basing it off regular season statistics that often correlate poorly with playoff results."

Regular season goal ratio actually predicts playoff success with reasonable accuracy.

Do you have any data that suggest otherwise?