In case you haven’t already I highly suggest you meandering over to the APBR analysis discussion group. There is a great dialogue going about what stats do and don’t tell us about basketball. To whet your appetite, I’m only going to give you a little piece of the first few exchanges, which nowhere gets into the depth of the discussion.
If you’re already sold, go to this page and read the first thread on the page (#3513). Just promise you’ll come back tomorrow ;-)
If you still need some selling, then I’ll start you off with an excerpt from the post that started it all.
Date: Thu Mar 25, 2004 10:30 pm
Subject: The Problem with Possessions-Based Linear Weights
…The second approach is what I will call the possessions-based approach. The essence of this approach is to count every contribution to either points scored or a failed possession and to count it only once. This is certainly the approach used to construct John Hollinger’s PER and its lies behind the construction of Dean Oliver’s offensive and defensive ratings. Also, a large fraction of the arguments on this board are about the proper way to do this possessions-based accounting.
So what is wrong with this approach? The problem is that there are numerous contributions to successful or failed possessions for which there are no statistics – a good pick, an ineffective blockout, a good entry pass that leads to a score but not an assist, the presence of a shot blocker that keeps his opponents from driving to the hoop. One could easily argue that the unmeasured contributions to successful or failed possessions are more than the measured contributions, e.g. points, assists, steals, etc…
Now mind you this is only 2 of about 20 paragraphs that were posted. The rest of Dan’s post spans a number of intelligent issues, including the NBA’s efficiency statistic, the difference between basketball and baseball statistics, possession based statistics, and linear weights. The first two to reply were Dean Oliver and Bob Chaikin, who within a half an hour of each other asked Dan the same question. They wanted him to “easily argue that the unmeasured contributions to successful or failed possessions are more than the measured contributions.”
…What do we measure on the offenive end?
1. We measure which player touched the ball last on every field goal attempt and we measure the outcome of those field goal attempts.
2. On successful attempts, we sometimes measure the player that touched the ball second to last.
3. We measure personal fouls on a particular player when those personal fouls lead to free throws and we measure the outcome of those free throws.
4. On failed field goal attempts, we measure the player who regains possession of the ball.
5. And finally, when possession turns from one team to the other without a field goal or free throw attempt, we measure who is responsible for that “turnover” of possession.
That is a lot and that is much better than what we measure on the defensive end. But what contributions to scoring or not scoring do we not measure?
1. We do not measure which players successfully navigate the ball to the frontcourt.
2. We do not measure which players initiate an offense with an effective non-assist pass. In fact, we fail to measure all of the non-assist passes that contribute to scoring (or non-scoring), such as all of the passes that lead to shooting fouls.
3. We do not measure which players get themselves open in out of bounds situations.
4. We do not measure screens on the ball or off the ball.
5. We do not measure which players keep the floor spaced leading to fewer turnovers and higher percentage field goal attempts. It is pretty tough to have a successful field goal attempt when you are
double teamed because of poor spacing.
6. We do not measure which players tend to hold onto the ball for an inordinate amount of time leading to forced shots or shot clock violations.
7. We do not measure which players correctly run plays and which ones do not.
8. We do not measure players failing to get open leading to a turnover for the player holding the ball.
9. We do not measure players with good hands grabbing an errant pass that would have been a turnover for the passer.
10. We do not measure the player who keeps a possession alive by tipping an offensive rebound to a teammate or by blocking out an effective defensive rebounder…
A few hours later Dean Oliver volleyed with:
Most of these unmeasured things aren’t that hard to accomplish (or to avoid, if they’re negative). I can go out and set picks. A lot of these 10 unmeasured things are taken as givens. Guys know how to do these things and, if they don’t, they aren’t as important as the measured things. That’s the conventional wisdom. Perhaps not right, but I think there is a significant burden in showing that these unmeasured factors are more important than the measured ones…Depends on how you make that list. It’s ALWAYS easier to make a longer list of unmeasured things than measured things. For baseball, things that affect whether a run is being scored:
1. The signs flashed by the 3rd base coach.
2. Whether the man on first is running on the pitch or not.
3. Whether the man on first saw the signs.
4. How the fielders are positioned (now starting to get measured).
5. Whether the hitter has that black stuff under his eyes or not.
6. Whether the pitcher is in the sun and the hitter is in the shade.
7. How good the hitter is at reading speed of pitches.
8. How fast a hitter gets out of the batter’s box.
9. Whether the hitter is swinging for the fences or for a base hit.
My point is that you can break down the games of baseball or basketball to an infinite degree. I think baseball and basketball offenses are broken down pretty well by stats. What’s left over are small variations of strategy or training. Do they matter? Yes, but do we miss a significant amount of value by not measuring them? I don’t think so…
I really don’t want to go any further, because I’ve paraphrased enough. It’s such a great conversation that continues with some interesting twists that I won’t get into. I recommend going there & reading through the posts, or you won’t know what you’re missing. You know it’s a good post when a few more threads have stemmed from it, including “List of unmeasured stuff to track”, and “The Knowledgeable guys…”