Tag Archives: NBA

The MVP debate, part II

We often think of players’ boxscore statistics in terms of cumulative sums or averages, but these statistics, while they tell us about prolificness and what one might expect from any player in a given game, tell us very little else about the player’s output. Consider three hypothetical players in an 82 game season: Player A scores 5 points in 41 of his games, and 35 points in the other 41 games, player B scores 20 points in each of the 82 games, and player C scores 19 points in 80 of his games, and scores 60 in each of the remaining two. Each of these players ends the season averaging 20 ppg, each scored a total of 1,640 points. However, there should be no question that they are very different players, even without considering non-scoring contributions. B is extremely consistent, C is pretty consistent but has rare scoring outbursts, and A is either a big threat or hardly a threat at all. (Please keep in mind that I could be doing the same with per-minute statistics–it’s just a little easier conceptually to discuss per-game stats, while making an equivalent point.) Opposing teams would need to plan differently when facing each of these three players, and their value to their own team is a function not only of their scoring average, but their entire scoring distribution. Since it is much easier to keep track of cumulative totals, and since the simple mean can be calculated by dividing total points (ast, reb, etc.) by total games, we have all been raised on means and sums–which are useful as far as they go, but don’t tell the whole story. So, into the plethora of other “modern” statistics, I would like to add several statistics that have been with us the entire time, but hidden behind season sums and means: the standard deviation, the geometric mean, and the distribution.

The standad deviation is a summary statistic like the mean, but it measures dispersion. Essentially, it attempts to capture the typical deviance from the mean of each data point. So, players whose per-game boxscore stats vary a lot from game-to-game will have a higher standard deviation than will players who are more consistently close to their own mean. Whether a high or low standard deviation is a good thing is a normative question, although I tend to think that consistency (indicated by a low standard deviation) is a good thing. Bear in mind also, that typically, the greater the mean, the more room there is for variance, and thus the more potential for a larger standard deviation. Thus, another statistic, the coefficient of variation, can be used to give an idea of variation while controlling for the magnitude of the mean.

The geometric mean is similar to the arithmetic mean, in that it is a measure of centrality. However, it seems to emphasize consistency more than does a simple arithmetic mean. Where the arithmetic mean is the sum of the data divided by the number of data points, the geometric mean is the product of the data exponentiated by the inverse of the number of data points. Thus, in our above example, each player has the same mean (20 ppg), but B has a geometric mean of 20, C’s is 19.54, and A’s is 13.23. According to the geometric mean, then, player A is valued almost exactly the same as player D, who scores 13 points in each of 63 games, and 14 points in every other game. Both of their g.means are around 13.23, but player A’s arithmetic mean is 20, while player D’s is 13.23. As such, the geometric mean, especially when presented alongside the arithmetic mean, may tell us even more about a player’s output.*

Finally, there is the entire distribution of per-game point totals. This encapsulates all of the information about a player’s production, because it is the player’s entire production. It’s not a numerical statistic, but can be represented as a graphic, or even (theoretically) an equation. The distribution is represents essentially the same thing as does a histogram or bar chart of each statistic’s frequency at each level of output. In the graphic below, I display each of four players’ distributions on six different per-game statistics. This should give the viewer a very complete idea of each players’ production. I also include the summary statistics I’ve described, which individually give some information about the distribution, and taken together represent a partial but informative view of player production.

mvpdensities.png

This graphic presents the output of four potential MVP candidates through about 60 games of this season. Note that LeBron James tops Kobe Bryant in arithmetic means across every category, and seems to be a more consistent scorer (on a per-game level, at least)… I hope you find this depiction of production useful and informative–please don’t hesitate to participate in the ongoing MVP debate (see this post).

* A note about geometric means: since a player might have zero points, or assists or blocks, etc. in any given game, there is the potential that this zero would “wipe out” their geometric mean for that statistic, making it relatively uninformative. Thus, I have replaced each instance of 0 with 0.9 — which penalizes the player for having a low figure, but maintains valuable information. This is probably not a perfect solution, but I’ve applied it consistently, so it should at least be “fair” in some sense. Let me know in the comments if there is a better way of doing this.

NBA Players in their prime

It has been suggested that I look at players’ statistics from only the primes of their careers. This is a good idea, given that both very inexperienced and very old players will “regress to the mean” in terms of their performance and possibly, playing style. As such, I generated a sum of each player’s boxscore statistics during the modern area across only their best seasons. My definition of “best” was simple: not their worst. For each player, I found their mean seasonal winshr, as well as their winshr standard deviations. Any seasons for which a player’s winshr was greater than the mean less one standard deviation was included in this analysis. This way, I excluded seasons in which a player was injured or relatively underused because of age or because of a minor role on their team. Chris Webber’s current and previous seasons, for example, would not be included. In this way, I hope to get at the “pure” essence of each player for an even better comparison. You will probably not be surprised to see that the diagram looks very similar to the non-peak-performance versions:

nbaprimethumb.png  NBA players at peak performance [pdf]

 A few interesting things to note, however: at their peak, Michael Jordan and Larry Bird are now among each others’ closest matches. Also, taking a macro view of the whole network, it is now easy to identify several different nodes: In bluish purple at top left, we can see defensive-minded, “dirty work” bigs, while at the bottom in blue are more scoring bigs. To their right is a reddish group of primarily scorers, while going north from there in green we see “pure point guards” and then more scoring point guards. Etc, etc. Let me know if you notice any other interesting connections or clusters in the comments.

          Network diagram example code

          I’ve had requests for my data and for the code I used to make these plots. So, in the spirit of openness, I’m posting them. If you would like to use them, please adhere to the Creative Commons license I’ve chosen, and let me know what you come up with. The .csv is the top 1000 careers over the last quarter century-or-so, determined by a playing-time-based statistic, and the .R file will run in R, and requires you to install the package sna. The sna package is awesome, it makes network diagramming essentially idiot-proof. Note that I currently have this code writing to a PDF, and that it cannot write to the pdf if a pdf with the same filename is open. Also, remember to make sure you change the csv’s file directory in the R code, or it won’t ever work. Please let me know if it’s not working for you, or if you know of a more efficient way of doing the same thing.

          1000 Top Careers [csv]

          Network Diagram Example [R]

          NBA season network diagram

          It  was suggested that I compare players on single season data, rather than career sum data, both as a validity test and to gain other insight. It goes without saying that players’ styles change over their career–often, scorers become less effective and try to do other things well. Sometimes (as with Jordan, for example), we see players add dimensions to their game over time. So, I present yet another network diagram, one which illustrates the changing nature of each player. A few notes: this set is somewhat scorer-heavy, because of the way I generated the list of best seasons (using a euclidean distance metric). Also, when looking at this, it helps to keep in mind that this is a two-dimensional rendering of a hyperdimensional network–unless players are actually connected, visual proximity doesn’t necessarily mean anything, although it may not mean nothing. It would appear, given the degree to which players’ seasons cluster together, that the proximity algorithm functions fairly well.

          NBA Seasons Proximity Network [PDF]

          Toward a basketball taxonomy

          I hope this isn’t getting repetitive, because I’ve got a diagram that will blow your mind: it’s like the entire NBA in a petri dish, with all different phyla and genera of player types represented. I used the same methodology I’ve been using (with the per-minute, rather than ratio statistics), but generated the graph with fewer connections (just the single closest match) per player. As a result, there are a whole lot of isolated clusters instead of one completely interconnected network. Also, I went ahead and did 1,000 players at once, instead of the standard 250. What I got astounded me–they look like microorganisms swimming around on the microscope slide that is the NBA. I apologize for the tiny font–if you zoom in to 125%, it should be readable–but had I made the names any larger, they would have overlapped to an illegible degree.

          nbapetrithumb.png The NBA “petri dish” diagram [pdf]

          I would be very interested in collectively coming up with a sort of “baller’s taxonomy,” wherein we try and identify the different clusters using some more subjective terms. I think we could come up with a better vocabulary to describe players and define playing styles. If you have any ideas, please put them in the comments, and if there is sufficient interest, I may come up with a more formalized process, in the hopes of putting together a follow-up diagram with labels.

           

          Since I had already run the algorithm anyway (it takes a lot of cycles to do 1,000 players), I went ahead and made a completely connected version of the 1,000 player diagram. Warning: this one is pretty hard to parse.

          nba1000thumb.png 1000 player network diagram [pdf]

          Keep in mind that the search function (ctrl-f) will be really useful for these.