I'm not sure I can find the study now, but kevin Pelton did one a few years ago, i forget all the details, but the idea was it seemed like guys improved more in the nba than in college. Will try and find
Pelton: NBA develops players better
story is for insiders only. Hopefully it's cool if I post this excerpt
Although we can't run an experiment on how things would be different with a higher age limit, there is a group of relevant prospects we can use as a point of comparison: players who chose to return to school for their sophomore seasons. Specifically, I looked at players from the past five drafts who were in Chad Ford's top 30 the summer before their sophomore year and ultimately were drafted in the first round. Not all of these players would have been first-round picks had they turned pro as freshmen, but many of them -- notably
Jared Sullinger,
Harrison Barnes and
Cody Zeller -- passed up the chance to go in the lottery.
As a control group, I used players who actually were one-and-done from the equivalent recruiting classes, covering the 2008-12 drafts. This group is somewhat more talented -- it includes four of the five No. 1 picks -- but the sophomores are strong in their own right. Of the 14 sophomores who qualify, 12 went in the lottery, and James Harden and Paul George are now All-NBA contributors.
We're not interested in the overall performance of these groups anyway. Instead, we want to focus on how they developed year to year. That's where my NCAA-to-NBA translations come in handy. They allow us to put college and NBA performance on the same scale (using player win percentage, the per-minute component of
my WARP rating that is equivalent to PER).
That shows something remarkable. On average, the sophomores who returned performed only marginally better than they did as freshmen.
Sophomore development (player win pct.)
Amazingly, of the 14 sophomores who qualify (which requires playing at least 500 minutes all three seasons, a criterion that knocks out
Blake Griffin, among others), nine rated worse as sophomores than freshmen. That includes basically all the high-profile freshmen who passed on the draft and saw their stock fall.