NBA Lottery Picks From 1995 - 2020

Introduction

I've been really interested in plotting and visualizing different NBA trends throughout this Thanksgiving break. Recently, I have been wanting to fact-check a common axiom I hear around the NBA during draft season: the notion that *older* draft prospects tend to have have *lower* upside. This is such a widespread belief that it can be heard on all levels, from NBA fan discussion on r/nba, to media draft analysis, to even GMs speaking about their draft choices.

For this visualization, I calculated the age of every lottery pick in the NBA draft from 1995 - 2015. I started at 1995 since this was the first modern "prep-to-pro" year with Kevin Garnett jumping from high school to the NBA. I ended at 2015 since I don't think we can develop an accurate read on the career trajectory of draft picks chosen after 2015 yet.

For each age range, I plotted a boxplot to visualize the distribution of the players' career PER, WS/48, BPM, and VORP. Let me know if you prefer to see another stat included here - I just went with the ones that Basketball Reference had publicly available.

Data

Here is the link to my plot

Key Results and Conclusions

Minimal differences among 18-21 year old prospects

It seems that differences in "upside" among 18-21 year old prospects are largely contrived by our brain's intuition, since there do not appear to be any significant difference in performance or success in the NBA for 18-19 year olds when compared to 19-20 and 20-21 year olds. Although VORP shows that the best of the best players since 1995 have been those drafted at age 18-19, the variation in distribution of BPM, WS/48, and career PER data is much lower.

Thus, we should be a lot more careful when assigning more favorable grades to extremely young prospects because they don't seem to have markedly better careers when compared to their slightly older counterparts. (Example: The data shows that 20.8 year old Donovan Mitchell would not have any different upside than 18.9 year old Kevin Knox)

Lower Extreme values for 22+ year old prospects

Interestingly, it looks like the median production is not really affected by the age of the prospect selected at all. However, there are some clear differences in the extremes.

The collective distribution of 22 and 23 year old lottery prospects shows that they tend to have much lower upper quartiles and extreme values, thus the best-case scenarios for these types of players is not as exciting. Although this difference is not as pronounced for 18-21 year olds, there is a huge drop off in the upper extreme values when moving from the 21-22 year old range to the 22-23 range.

Contrary to many other contexts, the NBA draft is a lot more about the outliers than it is about the median selection - each team is gambling on their pick becoming a future Tim Duncan or Dirk Nowitzki, and a successful draft would mean finding a franchise player-level talent. Therefore, our final conclusion is that although there are minimal differences in upside when comparing prospects in the 18-21 age range, 22+ year old prospects tend to have markedly lower ceilings than their younger peers.

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Acknowledgements/Notes

• Data was scraped from basketball reference (player pages, draft pages, advanced stats pages) as well as wikipedia (specific dates of each draft for age calculation). Scraping was done using beautiful soup.
• Figures were processed using numpy/pandas and visualized in matplotlib.
• Sample sizes for each age range: