## October 26, 2006

### Strength of Opposition II

I still have my doubts about strength of opposition. I went through every team picking out the top forward on the team (mostly based on points and even strength ice time). At this point my list could be quite imperfect. Using simple statistics I was able to calculated expected ice time with another player. For example the probability player 1 is on the ice is 25% and the other player is 33% suggests that if those two variables are random and independent they would spend 8.25% of the game together, so if a player plays more than that against the top players then we could say he’s getting a tougher opposition. One can easily compare the ratio of actual percentage together vs. real percentage together, so for example if the above players actually spent 10% of the game together then they would’ve spent 20% more time together than expected.

So using a “measuring” player (not sure I have the best set yet) from each team I can sum up total even strength time, total time by a given player and then sum up the total time of my measuring player. I get an average of the percentage of even strength time of the player and top opposition percentage. I can simply compare that to the expected time vs. actual time. The results were a little surprisingly useless the most “abused” players only received 4% more difficult opposition (all from same team: Florida). The most protected player was Ryan Sutter of the Nashville Predators with a rating of -5%, this would suggest his statistics are off by -5% multiplied by the relative difference between the top players and average players (if 3 times better than average players than the easier opposition is making their statistics appear 15% better than they should be). However 95% of the players are within 2% of 1, so most players are seeing tougher opposition 2% more often than expected (only affect their statistics by 6% if top players are 3 times better than average). This would be indistinguishable.

I'm not saying people don't try, in fact Bourdon for example has had the easiest opposition on the Canucks. It's just tough to get significant scores when the opposition is trying to do the opposite as you are (get good players out against your bad players) and you have to deal with the physical limitations of your personnel. I have never seen convincing proof that this exists. Doesn't mean I wont keep looking, but I think I can at least attempt to build a model without worrying about opposition and just worrying about teams lines and strength of the opposing team.

David Johnson said...

I have to disagree. I do think that opposition and line matching makes a big difference. The biggest argument for that claim is that home teams win 55% of the time. That is a fairly significant advantage. And what is the biggest advantage that home teams get? A greater ability to match lines because the road team has to put their line on the ice first.

I am currently working on developing a player ranking system which considers every player the player has played with and against to come up with offense rankings, defense rankings and overall rankings. The results I have seen so far are somewhat surprising but also somewhat make sense when you really begin to think about what is happening. I hope to make a post on my blog in the next day or two with some initial results.

The Puck Stops Here said...

There are other harder to quantify advantages that are at least as big as the last change.

Eating and living at home, vs out of a suitcase in a hotel. Not having travelled last night is an advantage (for teams involved in homestands). Having the fans on your side in the area. Knowing the nuances of the rink in better detail than the opposition.

All of this factors into home ice advantage.

David Johnson said...

It would be interesting to try to quantify some of these There are certainly times in which the home team played the night before on the road. What is the record of the home team in these situations? Does the western conference have a more dramatic home/road difference than the east where generally travel is more difficult?

JavaGeek said...

Don't worry I'll have a nice interesting post regarding these things up today...

Jeff J said...

A good test of the importance of last change would be to compare the home team's win % (as a fraction of a std. deviation) to that in other sports where they *don't* get last change.