Before the season started I predicted that the Boston Celtics would defeat the San Antonio Spurs in the NBA Finals. This prediction was motivated by two issues.
1. My forecast – which required that I guess how many minutes each player would play – indicated that Celtics were clearly the best team in the East and the Spurs were probably the best team in the West.
2. I thought it would be interesting if Bill Simmons – who argued last spring that Tim Duncan was clearly better than Kevin Garnett – got to root for KG and his Celtics against Duncan.
And of course, #2 was more important than #1. :)
Each Team at the 33% Mark
As I write, each team is about 1/3 of the way through the regular season. And at this point, each team is currently the best in their respective conference. As expected, the Celtics are clearly better than any team in the East. And the Spurs are only slightly better than any team in the West.
On the surface it looks like each team is performing as we would expect given what the players on each team did last year. But when we look at the current projection for each team this season – reported in Table One — we see that the Celtics look quite different from what we would have expected in October.
Table One actually offers two projections of the Celtics and Spurs in 2007-08. The first looks at how many wins we could expect if each player plays as well as he did last year. This is the same as the pre-season projection, except now we have a better idea of how many minutes each player is going to play. The second estimates how many wins each player will produce if he keeps playing as well as he has this season.
The Spurs Story
For the Spurs, each projection is basically the same. Last year this team was led by Tim Duncan, Manu Ginobili, Tony Parker, and Brent Barry. This year, each of these players is again very productive.
The one surprise is Fabricio Oberto. Last year he posted a 0.117 WP48 [Wins Produced per 48 minutes]; a mark that’s slightly above average. This year his shooting efficiency and rebounds have increased while his turnovers have declined. Consequently his WP48 has risen to 0.242. Although his minutes are limited, this substantial increase in per-minute performance does improve the team. And that improvement would show itself in the standings if this team could manage to stay healthy. Unfortunately, each of the big four on this team has already missed a game. If injuries continue to be a problem, the Spurs might have trouble reaching the Finals.
The Celtics Story
Beyond the play of Oberto, the Spurs of this year – when healthy — look very much like the Spurs of last year. The same story cannot be told of the Celtics.
Last year the Celtics only won 24 games, the second worst mark in the Association. In the off-season, though, the team added Kevin Garnett, Ray Allen, and James Posey; three players who were above average last year. With this talent added to Paul Pierce and Rajon Rondo, it was expected this team would rise to the top of the conference.
In fact it was expected that this team would be competitive with the defending champions. The Spurs projected wins – based on last year’s performance – was about 63 wins. Given what Boston’s players did last year, we would expect this team to win about 64 games. Again, this mark would just about match the Spurs and clearly lead the Eastern Conference.
Although the Celtics are clearly on top of the conference, the team has gone beyond leading the East to crushing the league. Boston has already matched last season’s victory total, winning 24 of its first 27 games. Such a pace is consistent with a team winning 73 regular season games. And when we look at efficiency differential – offensive efficiency minus defensive efficiency — the team looks even better.
The Bulls in 1995-96 won 72 games and posted a differential of 13.0. This is the best mark in the league since 1973-74. The Celtics currently have a differential of 14.9. Yes, the current Celtics are posting a better mark than the team considered the best in NBA history. To give this result even more perspective, the Spurs differential this season is 6.9 (which is very good). Still the Spurs mark is only about half of what we see from Boston.
The Celtics efficiency differential, which is a mark outside of our previous observations of the NBA, gives us a wins projection that is – not surprisingly – also outside our previous observations. Currently the Celtics are projected to win about 78 games. Given that this team has already lost three times, this projection is obviously too optimistic.
Before I get to what this means, let’s quickly review why the Celtics improved. A big part of this improvement comes from the play of Kevin Garnett. If Garnett repeated what he did last year in Minnesota, he would be posting a WP48 of 0.330 and be on his way to producing 19.9 wins. Each of these marks is very good, yet short of what he is doing this year (0.405 WP48 and 24.4 projected wins). Although we might see this as KG improving, it’s perhaps better to think of this as Garnett returning to what he was before the disaster that was 2006-07. If you recall, the Timberwolves changed coaches in the midst of last season in a vain hope of returning to the playoffs with Garnett. As noted at the time, the talent around KG was simply not that good in Minnesota. So playoff contention was not realistic.
Before the turmoil of last season, Garnett posted a 0.430 WP48 and produced 26.5 wins in 2005-06. If Garnett repeated that performance this season, and no one else improved, the Celtics would be on pace to win about 70 games this season.
Of course, about 70 is not the same as 78. When we look at Ray Allen, Paul Pierce, and Rajon Rondo we see that what we saw last year is pretty much what we are seeing this year. To see how the Celtics move from 70 to 78 projected wins, we have to turn to a player I didn’t think was going to help much, Eddie House.
Prior to this season, House had played seven NBA seasons for seven different teams. Across this career he had never posted an above average WP48 and had only offered 2.5 Wins Produced. This year, though, House has a much higher shooting efficiency, has grabbed more rebounds, and is getting more steals. As a result, he has already produced about two wins and is on pace to produce over six for the season.
What Does 78 Mean?
Okay, so we see that Garnett and House have led this team from a projection of 64 to 78 wins. What exactly does a forecast of 78 wins mean?
Jason Eshleman – a UC Davis anthropologist who often leaves comments in this forum (and authored a post on the Rockets a few days ago) – often reminds people in the comments that you cannot evaluate models by considering events outside what the model considers possible. In other words, it’s not important what Wins Produced tells us a team of Allen Iversons would do since we are never going to see an NBA team only employ a collection of speedy diminutive guards.
This lesson is important to remember when we look at the Celtics this year. The model predicts that a team with an efficiency differential of 14.9 would win almost every game the team plays. Clearly that’s not going to happen. The Celtics have already lost three times. Unfortunately, the data used to estimate the model did not include any team that was this much better than the Bulls of 95-96. So we should not be shocked that an observation outside the data the model was based on would give us such an odd result.
That being said, the projection of the Celtics may not be that far off. As noted, a 24-3 team is on pace to win 72 games. If the model says 78, and the team wins 72, such an error is not really that large.
Let me close by noting that I am not sure the Celtics are going to win even 72 games. The key players are still Garnett, Pierce, and Ray Allen. And these players entered the season old and are not getting any younger. An injury to any of these players would easily derail the Boston train. Of course, without such an injury, this train is headed for this team’s first title since 1986. Such a title would be sweet redemption for the much maligned Danny Ainge (general manager), Doc Rivers (head coach), and of course, Kevin Garnett.
Our research on the NBA was summarized HERE.
Wins Produced, Win Score, and PAWSmin are also discussed in the following posts:
Finally, A Guide to Evaluating Models contains useful hints on how to interpret and evaluate statistical models.