“I came out of Bataan and I shall return”-Douglas MacArthur on arriving in Australia in 1942
One of the interesting side effects of changing jobs is losing my laptop. I turned it in on Friday and since then I’ve felt like I’m missing an arm. I’ve been working on my wife’s laptop (which is a less than ideal scenario for all involved) and it’s kinda sucked. Yesterday’s piece took about four times as long as normal, while I adapted to my new writing/number crunching scenario reality. But I adapted and I persevered.
Let’s get back to work.
You Big Baby
Probability of Home team winning a game (Win %)
= (Projected Wins Home Team-Projected Wins Road Team)/82 +.606
=Win %: (Proj. Home Team Win% – Proj. Road Team Win%) +HCA(.606)
You’ve seen this before on this blog (Go here for the Basics). This is the simple equation I came up with for the home team winning a single game (see here for detail). I’ve used this for the evaluation of our predictions among other things (see here) and it does a pretty good job.
But you know by now that pretty good just doesn’t cut it.
We're all about excellence
When I first worked out Homecourt advantage I simply went looking for available data. The data set was the percentage from regular season games from 1999 thru 2008 (in which the home team wins 60.6% of time) and as I said before this was good and worked fairly well. A number of my readers have made many suggestions. Here’s the list of things that I’m going to do here:
- Add in the effect of rest days and back to backs.
- Add in the effect of altitude
- Use a more recent data set.
The first thing to do is build the data set. For that I turned to our old friend over at dougstats .
Dude, thanks for the info
I downloaded every game for the last five years (and before you ask see here ). And I went about adding the rest days and altitude. I did that as follows:
- For rest days, I chose three levels:
- 0 for back to backs
- 1 for day of rest between games
- 2 for >2 days of rest
- For Altitude, I also chose three levels:
- Zero to low elevation (430′ or below): Boston, LA, Memphis, Miami, New Orleans, Sacramento,New York City,Orlando,Dallas,New Jersey,Toronto,Houston,Seattle(gone but not forgotten),Portland,Golden State and Washington (hi Ted!)
- Some elevation (430′-1117′): Charlotte (Jordan with just some elevation seems wrong somehow), Milwaukee, Chicago, Cleveland, Atlanta, Indiana, Detroit, San Antonio, Phoenix, Minnesota
-
Nosebleed Country (5300-9400′): Denver and Utah
Now, If I simply work out the percentages here I won’t account for the strength of the opponent. Luckily, we already know the formula for two opponents on a neutral court:
Probability of Team A beating Team B at a neutral site = (Raw Win Production Team A (Sum of ADJP48*MP/48 for all players on team) -Raw Win Production Team B (Sum of ADJP48*MP/48 for all players on team))/82 +.500
So if I use the total raw win numbers for each team for the season to calculate the win probability for each game if it was played at a neutral site, I can average it out (through the magic of large sample sizes) and figure the homecourt advantage in each scenario over playing at a neutral site. That table looks like so:
If I add in .500:
Some interesting findings. Both, altitude and rest days affect the Homecourt advantage and they interact with one another. Average HCA is at 59.9%. Altitude is directly proportional to HCA . Rest days are a little stranger. Altitude directly interacts with rest. Denver and Utah kill teams at home if they have a rest edge but they get killed themselves if the other team is coming in with at least a two day rest edge.
Tomorrow, I give you power rankings.
Arturo's Silly Little Stats v2.0 
Alvy
11/08/2010
arturo,
on thrusday, the lakers will go to denver. both teams by then will of had two days of rest. does this suggest denver will enter the contest with a home winning percentage of 60? i want the lakers to go undefeated as long as possible >:o
arturogalletti
11/08/2010
HCA for denver in that scenario is 77.8%.
Eliot
11/08/2010
Nice work! The rest day factor for the high altitude games is really interesting, I had no idea it had such a big effect on team performance.
arturogalletti
11/09/2010
Neither did I. I love surprising results.
Dan
11/09/2010
It looks like your sample size is too small, at least for the high altitude teams. It doesn’t make sense for there to be such a huge difference between games where the road team had 1 day of rest and games where they had 2+ days of rest, with the direction of that difference flipping depending on how much rest the home team had. Getting 2+ days of rest rather than only 1 gives the road team a 26% advantage if the home team has 0 rest (61.8-35.7), but it gives them a 24% disadvantage if the home team has 2+ rest (53.3-77.8).
Fred Bush
11/09/2010
If you’re tired, you can’t handle the altitude. If your opponent is less tired, you’re hosed.
Spider Jerusalem
11/09/2010
Seattle
😦
Devin Dignam
11/09/2010
So high-altitude teams should probably slow down the tempo when they have no rest and are facing a well-rested team. And they might even be able to increase their already large advantage by playing at a faster tempo in all the other situations…or just be happy with the advantage they have and leave pace unchanged.
Devin Dignam
11/09/2010
Oh, and I don’t see OKC in the list of cities – did you include OKC games?
Switching computers is a bitch, isn’t it? I’ve been dealing with using multiple computers for months now.
Ben R.
11/13/2010
I had a thought about another possible tweak–what about teams going on extended road-trips? If a team is gone for 5 or 6 games, especially if they’re traveling long distances, I wonder if their play deteriorates a little in the last couple games (or, on a smaller note even, if a single road game a few thousand miles away has a larger effect than a road game nearby)? Though, sometimes I feel like teams win the first few on a road trip and carry some momentum going into the last couple (then again, I’m aware that concepts like “momentum” often don’t really exist, and are just a mirage of random luck being more clumpy than you’d normally think–so maybe that part is just me being stupid).
I love the piece (and your work in general!), and if someone already mentioned this then my bad. I was just curious if that might be another possible upgrade to the homecourt advantage analysis.
Ben R.
11/13/2010
Also, I know what I mentioned would probably be a tremendous pain in the ass…