Looking Back at the NBA Draft, Part One

The NBA Draft was two weeks ago. Before the draft Erich Doerr offered a few thoughts on which players teams should consider or avoid. Now that the draft is in the books we can now focus our full attention on the players actually selected.

Of the 60 players chosen, 47 players played college basketball last season. So we have some information on these players. But how good is this information?

My answer to this question is going to come in two parts. Today I am going to review the 2006 NBA Draft. Tomorrow I will look at the players selected last month.

Draft Research

Analyzing the NBA Draft has been a part of my research agenda for a few years. So far I have two conference presentations to show for this effort. My hope is to do quite a bit more this summer. Of course, ideally I would have done quite a bit more before the draft this year, but other commitments got in the way.

Although I have been looking at this for years, my research on the topic is still far from complete. Here are some tidbits I have learned so far.

First of all, there is a statistical relationship between what a player does his last year in college and what he does his first year in the NBA. Specifically, from 1994 to 2005 there is a 0.69 correlation between a player’s Win Score per minute his last year in college and his Win Score per minute his rookie season in the NBA. In other words, if we shift from correlation coefficient (or r) to r-squared, about 47% of what a player does on a per-minute basis his rookie season can be explained by what he did the previous season in college.

To put this in perspective, in The Wages of Wins we report that a baseball player’s OPS last season explains 33% of his OPS this season. This means the correlation coefficient between OPS this year and last year is only 0.57. So college performance in basketball predicts a rookie’s NBA performance better than a veteran baseball player’s performance predicts his future production in Major League Baseball.

There is an apples and oranges issue in comparing basketball and baseball numbers. Still, I think one could argue that basketball numbers tell us more about the future than baseball numbers. In this sense, basketball numbers are better.

That being said, the numbers are not a crystal ball. Yes, there is a statistical relationship between what we see in college and the pros, but it’s not a perfect relationship. Or to put it another way… the college numbers tell us something, but not everything.

The 2006 NBA Draft

To see this point, consider the 2006 NBA draft. Back in May I reviewed the All-Rookie teams for the 2006-07 season. This analysis, repeated in Tables One and Two, indicates that the top rookies this past season were Rajon Rondo, Brandon Roy, Paul Milsap, Renaldo Balkman, and Craig Smith.

Table One: The 2007 All-Rookie Teams

Table Two: The 2007 All-Rookie Wins Produced Teams

Each of these player played college basketball in 2005-06. Could their performance have told us that these players were going to be the best rookies in 2006-07?

Table Three looks at the 26 rookies who both played college basketball in 2005-06 and at least 500 minutes in the NBA in 2006-07. The players are ranked in terms of their Position Adjusted Win Score per minute (PAWSmin) in college, as well as both their rookie season WP48 (Wins Produced per 48 minutes), and where they were taken in the draft.

Table Three: Reviewing the 2006 NBA Draft

From this table we see that each of the top five players in College PAWSmin finished in the top ten in WP48. In other words, just looking at the college numbers one could have suspected that Renaldo Balkman was going to be a productive pro (and that the New York fans should not have booed this selection).

Looking at the end of the list we see that none of the players ranked in the bottom ten in College PAWSmin finished in the top ten in WP48. In other word, Isiah Thomas – the same man who took Balkman – should have suspected that Mardy Collins might not be that productive in 2006-07.

Thomas should not feel too bad about these results. Overall we see that College PAWSmin is a better predictor of rookie performance than draft position. In sum, it does look like NBA decision-makers make mistakes in evaluating college players (so Isiah is not alone in making “mistakes”). The extent of these mistakes is what I will be looking into this summer.

For tomorrow, though, I want to look at the 2007 NBA draft. Which players are the best candidates to produce in 2007-08? Which players are not likely to help much next season? And did Isiah Thomas pick another winner last month?

Again, my answers will be posted tomorrow. Hopefully sometime this weekend I will get back to the discussion of position adjustments. Not sure there is much more to say on this topic, but I will offer at least one more post.

- DJ