The Value of One Statistic

I remember reading in some comment about the WNBA - by someone drunk on haterade - that a .420 average shooting percentage for the WNBA was weak and proof that the W was entirely second-rate, because a lot of NBA teams shoot better than .420. And of course, my computer at work denied me the chance to respond. The following shows what happens when you go by one statistic only to make your argument.


NBA Field Goal Percentage over Time

1946-47 .279
1947-48 .284
1948-49 .327
1949-50 .340
1950-51 .357
1951-52 .367
1952-53 .370
1953-54 .372
1954-55 .385
1955-56 .387
1956-57 .380
1957-58 .383
1958-59 .395
1959-60 .410
1960-61 .415
1961-62 .426
1962-63 .441

...

2007-08 .457

WNBA Field Goal Percentage Over Time

1997: .414
1998: .423
1999: .420
2000: .432
2001: .411
2002: .420
2003: .417
2004: .420
2005: .425
2006: .425
2007: .420

First, note that the current team average in shooting betwen a WNBA team and an NBA isn't much. Out of 100 shots made, an NBA team will make only three or four more baskets than an NBA team. You'd have to watch a lot of games over a lot of time to notice the difference.

Second, note how poorly teams in the NBA shot early in their history. This was the era when basketball was to other sports as the WNBA is to the NBA. Pro basketball didn't crack the WNBA worst league shooting percentage - .411 - until the 1960-61 NBA season. They didn't have a season that was better than any WNBA season until 1962-63.

Why did things change so much? I suspect two reasons - evolution and the changing nature of the game.

The first is evolution. Probably back in the late 1940s, there simply wasn't much known about proper basketball - what kind of plays to run, what to expect, what kind of players should be drafted and which released. A league has to evolve to the point where everyone knows what they should be doing - this is an argument from SABRMetricians like Bill James and scientists like Stephen Jay Gould. The art of running a proper pro franchise simply hadn't been perfected yet. As coaches and teams found out what worked and what didn't, shooting got better.

Compare this to the WNBA, where the shooting percentage seems to stay right around .420. Most women came into the WNBA "fully evolved" - they had the advantages that the men had in terms of training and pro play making, and simply infused the knowledge it took decades to learn into the game right at the beginning. By 1997, basketball as an art had sort of plateaued and the women came in at the top of the plateau. Barring some fundamental changes in rules, playmaking, training, or some quantum leap in strategy, .420 might be the upper limit of shooting in the WNBA.

The second change is the nature of the game. Frankly, back in the 1950s, players were shorter. You looked for the bounce pass and the layup. In the 1960s, the first wave of players to take advantage of their height and strength took over. The standard play then changed to the lob pass, with some airborne player slamming the ball in from above the rim. Height became at an even greater premium. More than likely, the 4 percent difference in field goal percentage can be explained by greater male height and strength.

I suspect this is also why NBA players appreciate the women's game. NBA players know they're taller and physically stronger and have greater vertical leaps. Most likely, they wonder what life would have been like if they had just been that much shorter or smaller, and they are reminded of the great ground-level games (and players) that they saw in high-school and college. If there's any ball player out there that knows that the game is not about the dunk, it's the NBA. I don't think I've heard of any NBA player disparaging the W, for the simple reason that they all know how hard it is to go out there and play at the pro level.

So if the WNBA is "weak", then a lot of players in the 1950s like George Mikan and Bob Cousy were "weak", too. You might be able to learn some things from a statistic, but you can't learn everything.

On the Value of Field Goal Percentage

The author of the Women's Sports Blog has been following the Pleasant Dreams blog. (Go to the blog. It's a good read.) However, the author is puzzled by the use of Wins Score and asks, "if Wins Score is a better metric than Efficiency because it doesn't take into account field goal percentage, then why do you report field goal percentage at all when talking about the Dream and the teams it plays?"

Let's first get into the details about field goal percentage and why some people like Wins Score better than Efficiency. The primary point is that to a certain degree, both are linear metrics -- each good thing you do gives you points; each bad thing you do loses you points.

Field goal percentage is equal to the number of field goals you make divided by the number of field goals you attempt. Therefore, any stat that is counting field goals made and field goals attempted is incorporating field goal percentage in some manner.

Both metrics count field goals attempted, but only Efficiency counts both field goals made and field goals attempted, whereas Wins Score skips the "field goals made" part completely, incorporating it into "Points". Why is this bad?

I'm going to repeat the article written by DJ at The Wages of Wins Journal. Let's look at, say, Chioma Nnamaka coming off the bench. She tries three field goals and makes one of them in her five or so minutes of play.

Efficiency has (Field Goal Attempts - Field Goals Made) and subtracts all of that from "Points". Nnamaka made two points. She had three attempts, and made one shot.

2 - (3 - 1) = 2 - 2 = 0.

So Nnamaka wasn't hurt at all by her 33 percent field goal percentage. It's an additive metric, so all we've done is add "zero" to the final total.

Let's assume she took four shots instead of three. One was a three pointer that went in, the other three were misses.

3 - (4 - 1) = 3 - 3 = 0.

In this case, Nnamaka isn't hurt by a 25 percent field goal percentage.

The problem is that these are very low percentages for success. The problem with Efficiency is not that it counts field goal percentage; the problem is that it places too high a value on it. In Effiency, anything above a 25-33 percent field goal percentage (depending on how many threes are taken) will be rewarded in the final results. This is a very very low standard to set.

Wins Score avoids the problem by not tallying up the number of field goals made. With Wins Score, field goal attempts are subtracted out, and Nnamaka would have earned 2 - 3 = -1 point for her crappy shooting.

Is Wins Score more reasonable than Efficiency? Part of the results have to do with a "smell test". I can count just about anything I want to, height, age, shoe size, add it up using some bizarre calculus and claim the results mean something. It would be circular reasoning to claim that the results verify what you set out to prove, when you claim that things are being added to or subtracted from the metric because they give you good results.

Wins Score passes the smell test to me more than Efficiency, which is why I use it.

(* * )

This then gets to the question, "So why are you including field goal percentages at all in the report if some metrics overvalue them?"
Victory". Efficiency and Wins Score are combined metrics and individual metrics. They are primarily designed to measure what one single player brings to a team, and they measure the totality of the combination.

Dean Oliver's Keys, however, looks at the entire team and is looking at pieces, not an entire combination. Efficiency and Wins Score says, "Which player has the best overall game?" and players can be compared across teams. The Four Keys to Victory ask, "what parts must an individual team do well to win an individual game?" They are essentially separate questions.

Field goal percentage is important at the individual game level because a team only gets a certain number of possessions during a game. Every time you take a shot, miss, and don't get the offensive rebound, you've given the other team a chance to score. If you miss a lot of shots, you give the other team a lot of chances to score. At the game level, it hurts.

However, in a way, both the Keys to Victory and Wins Score link up. Both say, "We're not going to reward a team/player for shooting 33 percent from the field." It's amazing how separate things begin to fit into a larger picture once you look at them. One problem that both Efficiency and Wins Score have is that neither values offensive rebounding very well, which Oliver's metric does.

I hope this answers the question. If it doesn't...well, I would go to blogs like Rethinking Basketball or Swanny's Stats or Storm Defense. There are a lot of guys who can explain this stuff better than I can.