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Friday, February 11, 2011

Ken Pomeroy Describes the Limitations of Plus/Minus

Plus/minus seems like a perfectly objective statistic and a very useful one for people who cannot watch every single minute of every single game (which would describe everyone, even though one blogger likes to pretend/brag that he alone has consumed every second of NBA action since sometime during the Bulls' three-peat glory days): you simply calculate the scoring differential when each player is on the court and, voila, you can see which players are having a positive impact and which players are having a negative impact; all of the hustle plays that are not captured by conventional box score numbers or even by "advanced stats" are presumably detected by plus/minus. Furthermore, adjusted plus/minus--which takes into account who else is on the court--seemingly refines the data even more.

However, anyone who has looked at a lot of plus/minus data immediately realizes that it is very "noisy": some players who even the "stat gurus" know are not that good inexplicably have impressive plus/minus numbers, while some players who are clearly above average do not have outstanding plus/minus numbers. At the very least it seems obvious that one needs a very large set of data to filter out this noise. "Stat guru" Ken Pomeroy recently devised a very interesting test of the limitations of plus/minus; his work focused on the college game but can clearly be applied to the NBA game as well. You can read a detailed description of his methodologies and results in A treatise on plus/minus but his conclusion should be embraced by anyone who is attempting to analyze basketball: "It's true plus-minus captures everything that's happening, but that includes a whole lot of random things that lead to a hoop or a stop. Things that have nothing to do with the ability of the player you want to analyze. In basketball analysis, we should be filtering out randomness, not embracing it." Pomeroy notes that because the professional season is much longer than the college season there may be "limited use" for adjusted plus/minus in the NBA but even in that case one probably needs at least two full seasons of data to make any meaningful evaluations; in other words, most of the stat-based articles (about "clutch performance," player ratings, MVP rankings, etc.) that are popping up like dandelions in an untended yard are using data sets that are far too small to form the basis for sweeping, definitive conclusions (I realize that not all of these articles are using plus/minus or advanced plus/minus data but there is even less reason to trust the accuracy of Berri's numbers or Hollinger's numbers--both of which are based on subjective formulas that can be tweaked to reach whatever conclusions the author desires--then there is to trust plus/minus data that truly is objective in some sense even if it is only potentially meaningful when the data set is very large).

Pomeroy's article represents the kind of frankly honest research/experimentation that all "stat gurus" should be doing; instead of brazenly declaring that their numbers are flawless while the observations of skilled talent evaluators are hopelessly biased, "stat gurus" should be in their labs (metaphorically speaking) trying to ascertain the strengths and limitations of their beloved formulas: if more of them would do that--instead of writing articles with catchy headlines so that certain high profile entertainment providers will link to them--then they could make a real contribution to better understanding basketball.

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posted by David Friedman @ 3:59 AM


Lakers Edge Celtics, Spoil Allen's Record-Setting Night

Ray Allen scored 12 first quarter points--including two three pointers to move past Reggie Miller into sole possession of first place on the career list for three pointers made--as the Boston Celtics cruised to a 27-20 first quarter lead over the L.A. Lakers. The Celtics eventually pushed that margin to 15 points but then Kobe Bryant erupted for 20 second half points and the Lakers emerged with a 92-86 win, their first victory of the season against a legitimate championship contender. "Statement game" is a somewhat overused phrase but, whatever you call it, at some point before the playoffs began the Lakers needed to prove that they could summon up the necessary concentration and effort to beat a top level squad.

Bryant finished with a game-high 23 points on 9-17 field goal shooting, plus five rebounds and four assists; he played 38 minutes, which is roughly four more than his season average and an indication of just how important this game was to Lakers Coach Phil Jackson, because there have been times this season when Jackson has left Bryant fiddling on the bench even as the Laker reserves were burning down Rome on the court. It is reasonable to expect that in the playoffs Bryant's minutes will receive a similar boost if necessary but during the regular season Jackson is following a version of Rick Mears' classic Indy 500 mantra that to win the race you first must have a working car at the end of the race; if Jackson runs Bryant into the ground during the regular season then the team's three-peat hopes will surely vanish but if the Lakers are smart enough and steady enough to finish with one of the top four records in the league (second in the West only to the streaking San Antonio Spurs) then they will be well positioned to claim a third straight championship.

Pau Gasol contributed 20 points, 10 rebounds and four assists. He looked soft and tentative early in the game--bobbling the ball every time Kendrick Perkins touched him and settling for some fadeaway shots--but eventually Gasol provided some much needed paint presence. Miller (who was one member of TNT's three man announcing crew) even called Gasol "Iron Man" (surely the first time that appellation has ever been applied to Gasol)--not in response to Gasol's solid play but rather because a freak collision between Gasol and Lamar Odom left Gasol unmarked while opening a gash on Odom's head that required several stitches to close. Odom shot just 4-12 from the field for 10 points but he snared a game-high 12 rebounds (though several of those boards were his own misses). Andrew Bynum tallied 16 points and nine rebounds.

Allen led the Celtics with 20 points but he was largely silent after his sparkling first quarter. The Celtics will make no excuses about this loss but they were undermanned due to the absences of Shaquille O'Neal, Jermaine O'Neal and Delonte West, three players who figure to be significant postseason contributors. Foul trouble further wrecked Boston's rotation, resulting in Rajon Rondo playing 44 minutes and requiring the seldom-used Von Wafer to play 20 minutes.

In the first half, Bryant worked hard to get his big men involved while he scored just three points on 1-3 field goal shooting but even though Gasol and Bynum each scored 12 points the Lakers trailed 53-45. TNT's Charles Barkley has repeatedly said that Kobe Bryant has "slowed down a lot" and at halftime Barkley added that he knows from personal experience what Bryant is going through: Barkley recalled that during his prime he could go wherever he wanted to on the court and score but that later in his career he had to keep pump faking to get off a shot, a change that Barkley noted in Bryant's game now. Barkley's observation is valid to some degree--and I don't think that this is the first season in which Bryant has been relying more frequently on pump fakes as opposed to explosiveness--but Bryant is hardly as broken down as Barkley was during his late career run in Houston. Bryant has already played as many career minutes as Michael Jordan had logged by the time he was a 39 year old Wizard but I think that Bryant's current explosiveness is roughly equivalent to Jordan's circa 1997 or 1998; Bryant can still blow by people and dunk and he is not noticeably hobbling the way that Jordan did as a Wizard (or the way that Bryant did last season when he was limited not by age but by a knee injury that ultimately required surgical repair). Bryant has indeed slowed down to some extent but unless he suffers an acute injury (as opposed to the chronic wear and tear that he clearly knows how to manage) there is little reason to think that his numbers--or, more importantly, his overall effectiveness--will be diminished at playoff time; over the past three playoff runs resulting in three trips to the NBA Finals and two championships, Kobe Bryant's playoff numbers have been remarkably similar to the numbers that Jordan posted during the Bulls' second three-peat and I expect that Bryant's 2011 playoff numbers will not decline from that level.

The Lakers took command in the second half as Bryant poured in 20 points on 8-14 field goal shooting. The Lakers' bench did a solid job of maintaining a slender lead while Bryant rested during the first part of the fourth quarter and then Bryant returned to action with guns blazing, bagging three straight buckets in less than two minutes (and eight points in the final 4:49 overall, plus a great dish to Gasol for an easy layup after the Celtics triple-teamed Bryant) to hold off a late charge by the Celtics. It is obviously true that the Lakers enjoy a size advantage against many teams but it is befuddling that many people do not recognize that a major reason that the Lakers can so effectively exploit this advantage is that it is very difficult to double team the Lakers' bigs because of how much Bryant threatens the defense. Gasol and Bynum receive much more single coverage than they would if they played without Bryant. It is also worth remembering that the Lakers' big man-focused offense in the first half resulted in an eight point deficit; however, the advantage of getting the big men the ball early is two-fold: it keeps them mentally involved in the game at both ends of the court and, as long as the score is reasonably close, it preserves Bryant's energy so that he can close out the game at the end (whether or not Bryant's heroics fit the definition of "clutch" prescribed by various "stat gurus"). Coach Jackson has often mentioned that he would like the Lakers to keep the game competitive enough in the first three quarters so that Bryant can take over in the fourth quarter and I recall an oft-played video clip from Jackson's Bulls days when he implored his team, "Don't leave Michael (Jordan) yet. It's not time."

Allen's three point milestone is a significant accomplishment; his 2562 career three pointers are not only two more than Miller's old record but they are more than 800 ahead of Jason Kidd's third place total. The 35 year old Allen is in excellent condition and is shooting a career-high .459 from long range this season, so he probably will ultimately obliterate Miller's standard. However, amidst the quite deserved appreciation that is being shown for Allen (and for Miller) it would be nice if some recognition were given to the league that popularized the three point shot and to the player who held the career three point field goal record even longer than Miller did. The ABA adopted the three point shot (which had previously been used in the short-lived ABL) but despite the ABA's reputation its players were not nearly as three point happy as current NBA players are; as I wrote in The Evolution of the Usage of the Three Point Shot, "The ABA is thought of as a run and gun league that featured guards launching three pointers from all angles, but ABA teams actually did not shoot that many three pointers--at least compared to NBA teams since the 1988-89 season." Louie Dampier--who spent most of his career with the Kentucky Colonels and helped the Hubie Brown-coached Colonels to win the 1975 ABA title--held the career NBA/ABA record for three point field goals made (794) until the 1992-93 season. Dampier deserves mention as one of the sport's great long range bombers; in 1968-69 he drained 199 threes for the Colonels and the next season he buried 198 shots behind the arc: not only did those individual single season records stand until 1994-95--when John Starks took advantage of the temporarily shortened NBA three point arc to make 217 threes--but no NBA team made more three pointers than Dampier's 199 until the 1986-87 Dallas Mavericks connected 241 times from long distance in the eighth season after the NBA began using the three point shot. Dampier currently ranks just 103rd on the career list for three pointers made but his career three point shooting percentage was a very respectable .358, just ahead of Kevin Durant's current career three point shooting percentage (though of course Durant's number could go up--or down--as his career progresses)--and Dampier made more career three pointers than Larry Bird, who finished with 649 (Dominique Wilkins--hardly a pure shooter--made 711 three pointers, a good example of how much more prevalent three point shooting became in the 1990s than it was during Bird's prime in the 1980s). It would not have taken anything away from Allen if TNT had shown a highlight montage depicting the evolution of the three point record from Dampier to Dale Ellis (who Miller mentioned briefly during the telecast) to Miller to Allen.

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posted by David Friedman @ 2:35 AM


Sunday, February 06, 2011

Kobe Bryant in the Clutch...the Rest of the Story

Much has been said recently about Kobe Bryant's proficiency in "clutch" situations. I offered my general take on this issue last year in an article titled Being a Clutch Player is More Significant than Just Making Clutch Shots.

An interesting article digs deeper into a much cited stat--that Kobe Bryant has made just six of 22 game-winning field goal attempts during his playoff career--and shows that when those 22 shots are placed into a larger context Bryant actually performed well overall and the Lakers were very successful for the most part even in the games when Bryant missed a late shot that could have potentially tied or won the contest. For instance--just to cite the most recent of Bryant's misses--it is more than a bit of a stretch to say that Bryant was not "clutch" after he produced 30 points, 11 rebounds and nine assists with just two turnovers in a 103-101 Lakers victory over the Suns in game five of the 2010 Western Conference Finals; Bryant's "sin" in this game (according to those who mindlessly categorize all late game shots the same way regardless of distance, time remaining, etc.) was that he missed a desperation three point heave with just two seconds left in the game: two Suns crowded Bryant to contest his shot, leaving Ron Artest free to gather the miss and convert the game-winning putback. Maybe someday the "stat gurus" will figure out that the defensive attention that Bryant draws creates scoring opportunities for Bryant's teammates. NBA TV's Chris Webber has shown a refreshingly clearheaded grasp of this concept in several recent comments, repeatedly declaring that all of the Lakers other than Bryant were "mere mortals" prior to coming to L.A. and they would be "mere mortals" now if they were not playing alongside Bryant.

I don't expect biased or foolish writers to ever figure this stuff out--but don't fans deserve better than the recycled, nonsensical garbage shoveled out by the "big names" who cover the NBA? Are there really no editors who have the sense/guts to buck the establishment, shock the world and provide a forum for someone who has not been officially vetted by the would-be Don of NBA blogging/writing? Or is ESPN going to ultimately achieve a Pravda-like monopoly on NBA coverage because so many people are afraid to challenge the self-proclaimed "Worldwide Leader" for fear of not being invited to blog for ESPN(Chicago/Boston/fill in the name of your hometown).com?

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posted by David Friedman @ 5:56 AM