I wrote a full blog post here if you are interested. The blog post has a bunch of charts, which is nice. As well as a richer discussion of my method. But the crux of the argument is here:
Most likely Monta will regress. But by how much? You can divide shot attempts into different categories: 0-5 feet, 5-9 feet, 10-14 feet, 15-19 feet, 20-24 feet, and free throws. Ellis has increased his scoring output in five of them. These five categories account for a 6.03 PPG increase in scoring (partially offset by a 1.86 PPG decrease in scoring in the other two categories). 62% of the 6.03 PPG increase comes from two areas: the 20-24 ft. shot and free throws. Of course, the increase from free throws is a good indicator of sustainability while the increase from the 20-24 ft. shot is a bad indicator of sustainability.
However, we should expect Ellis to improve his shooting ability. He's playing on a better team. The question is by how much should we expect Ellis to improve?
We can estimate expected improvement by looking at the difference between Devin Harris's FG% in Dallas and NJ during the season he was traded and the difference between Jason Terry's FG% in Dallas and Atlanta during his last season in Atlanta and first season in Dallas. It's far from perfect, but it's all we got.
If we assume that the Terry/Harris improvement is a good estimator of Ellis's expected improvement, and if we assume that Ellis's true shooting ability from the 5-9 feet range and 15-19 feet range (why these ranges are chosen is in my post) was reflected in his 07-08 season and not his 12-13 season, then we get 22.4 points per game.
What do you guys think? Regress? Improve? Stay the same?