On the independence of shooting

Long time, no post. I finally got around to putting together a newer, better database, which has box scores going back to 2002-2003, more accurate identification of each player's class year, and basic stuff like conference affiliation. Previously I'd looked at three point shooting since I assumed it was more independent of opposing team ability than two point shooting, and now with more data, I figured I'd take a look at how true this is. To do this, I decided to look at games between each conference as an easy proxy for team ability. All else equal, a Big East team should be much better than a team from the SWAC, and indeed they were, with 33 wins versus 1 loss over the past ten years. However, if three point shooting is independent of team strength, we should expect to see that both sides shot roughly the same percentage from three: inside the arc would be where the two teams separated themselves. The graph below shows the value of each of the three types of shots for all 1087 different conference pairings. (the Big Sky and Ivy League are the only two conferences not to have played a single game against each other over this time period)

And that blows everything to shreds. The slopes of the best fit line for twos and threes are virtually identical at .2481 and .2247, respectively. For free throws, that number dips to a still positive .08287 when looking at two trips to the line. Given the large score effects found by Ken Pomeroy, this shouldn't be surprising, but it reiterates that a shot made in November versus the Little Sisters of the Poor isn't nearly the same as a shot made during the heart of the conference season, even if it is a three pointer. It should also be noted that there is virtually zero correlation between non-conference winning percentage and shooting percentage during conference play.