Which Offensive Rate Stats Stay Consistent When a Player Changes Teams/Roles?
You'd better read this post from August if you haven't yet.
In it, I looked at the year-to-year correlation coefficients for various offensive rate stats (TS%, AST Rate, TOV Rate, FTA/FGA, & OReb%) when a player changed his role in the offense. Essentially, I concluded that offensive rebounding and assists are relatively immune to changes in a player's possession usage, foul-drawing & turnover avoidance are less immune, and scoring efficiency is the most prone to fluctuate with a role change.
Today I wanted to expand on that post by adding another variable into the mix: changing teams. Other than the new variable, though, this study's format is basically the same as in the first post -- except I used touches per minute rather than possession % to define a player's role, and I added Dean Oliver's Offensive Rating (ORtg) into the mix.
Here's the setup: Once again, I found every player from 1974-2010 who was between 24 and 34 years old and played at least 1,000 minutes in back-to-back seasons. I then sorted those players by the absolute change in their touches/min, and took the top quartile as my sample of players who changed roles. I also isolated players who played for a different team than they had the previous season, forming four groups: players who changed team & role; players who changed role only; players who changed team only; and players who changed neither team nor role. Finally, I ran correlation coefficients on the year-to-year offensive rate stat performances for each group:
The results:
Shooting/offensive efficiency is actually far more impacted when a player changes teams than when he changes roles. This suggests that a team's system, coaching effects, and teammate interactions play a much bigger role in determining shooting percentages than "skill curve" effects.
Assists are more dependent on role than team -- for obvious reasons, how much you have the ball in your hands is a major factor when it comes to how often you set up your teammates.
Turnovers, fouls drawn, and offensive rebounds are all more team-dependent than role-dependent, but the differences are nowhere near as drastic as those observed in shooting efficiency or assists.
For players with no major contextual changes, assists and offensive rebounds are relatively stable; foul-drawing and turnover avoidance are less consistent; and scoring efficiency is the least consistent of all. This mirrors the findings of the original study.
Finally, it bears mentioning that even at its least consistent (TS% for players who changed teams), NBA player performance is way more predictable than that of the NFL quarterbacks Jason Lisk looked at in the football study that inspired these posts.
Filed under: NBA, BB-Ref Blog