Fact or Fiction: Is College Free Throw Percentage Better Than College Three Point Percentage at Predicting Three Point Shooting Success In The NBA ?

BANG

A commonly held thought in NBA circles states that a college basketball player’s free throw percentage is a better measure of his future success as a three point shooter than his three point percentage. But is this true?

(Skip to results if you aren’t interested in how I got these numbers)


The Process

The data set contains the most prolific three point shooters in the NBA. Everyone on this list had to have made at least 1.5 threes per game in the 2016–2017 season, and had to have played in at least half of their team's’ games. The original list included 85 players. After that, everyone who had played overseas before coming to the NBA, or who had come to the league straight of high school were eliminated. Everyone who shot less than 2.5 free throws and 2.5 three pointers per game in college got cut. Each person must have played at least 30 games in their last season of college ball (save for Robert Covington, where the average of his last two seasons was used). These precautions ensured each player’s sample size would be large enough. All stats are from the athlete’s last year in college. The final list included 43 players. (Click here for the entire spreadsheet).

Steph Curry and Klay Thompson are good. Who knew.

I looked at three categories: college three point percentage, college free throw percentage, and NBA three point percentage. For each of the eligible players, I calculated what percentile they fell into when stacked up against the other 42. This is because because simply using free throw percentage and three point percentage would have produced confounding results; there is a much greater variance in free throw percentage than in three point percentage, therefore a comparative ranking would work better.

The spreadsheet found four percentiles: percentile that the player fell into for three point percentage in college, percentile the player fell into for free throw percentage in college, percentile the player fell into for three point percentage in the NBA, and, finally, the average of the college free throw percentile and the college three point percentile.

There are more players in the spreadsheet than this. This was just to make the numbers readable.

I tested each of the college percentiles against NBA three point percentiles to see which was the best indicator of future success. These were the graphs:

Using a trendline for the most accurate data set

Finally, I calculated r for each of the graphs. (r finds how correlated a data set is. 1 is 100% positive correlation, 0.7 is strongly positively correlated, with anything above 0.8 being considered very strongly positively correlated. 0 is no correlation.)

College 3pt vs NBA 3pt percentile: r=.6756

College ft vs NBA 3pt percentile: r=.7945

Average of college 3pt and NBA 3pt: r=.7961


The Results

Welcome back, non-readers! It is, in fact, true that college free throw percentage is a better indicator of NBA success from three than college three point percentage is. However, finding the average of the percentiles for college free throw percentage and college three point percentage is just as good a predictor (if not a slightly better one) as free throw percentage. Turns out, it pays to be good at both. It is important, however, to remember neither is a complete predictor of a three point percentage in the NBA.


The (Eligible) Lottery Picks

How could it ever miss?

To get projected three point percentages, I plugged the percentiles back into the equation that tested both the average of the three point percentile and free throw percentile, and the observed NBA three point percentage.

Note: These are to be taken with a (fairly large) grain of salt. Most of these guys won’t shoot this well in their first year, and most of the guys with percentiles around 25 or lower might shoot closer to 30% than the 36% the equations projected them to have.

Markelle Fultz

Percentile: 33.2
Projected 3pt %: 37.5%

Lonzo Ball

Percentile: 36.5
Projected 3pt %: 37.7%

Jayson Tatum

Percentile: 48.25
Projected 3pt %: 38.4%

Josh Jackson

Percentile: 10.7
Projected 3pt %: 36.3 (Probably lower)

Jonathan Isaac

Percentile: 26.15
Projected 3pt %: 37.1%

Lauri Markkanen

Percentile: 76.5
Projected 3pt %: 39.9%

Dennis Smith Jr.

Percentile: 22.29
Projected 3pt %: 36.9% (Probably lower)

Malik Monk

Percentile: 55.4
Projected 3pt %: 38.7%

Luke Kennard

Percentile: 81.8
Projected 3pt %: 40.2%

Donovan Mitchell

Percentile: 34.5
Projected 3pt %: 37.6%

A final reminder: These aren’t definitive predictions! Players can improve (or regress) once they reach the NBA! I also want to quickly point out that three point percentage doesn’t paint the full picture of beyond-the-arc success; James Harden, regarded as one of the best shooters in the league, shot 34.7% from three this season, yet with an astronomical number of attempts.

Thanks to http://www.basketball-reference.com/ & http://stats.nba.com/