TRACER is an Elo-based rating system for the NBA, calculating a single number for every team after every game, going back to the 1995–96 season. An Elo rating is a predictive system that calculates the probability of who will win a game based on both teams' current ratings.
Pulse and Echo ratings are identical in calculation. The only difference is how they handle season-to-season carryover. The Pulse rating is an in-season snapshot only. Every team begins the season with an identical rating, and only the games in that season affect it. The Echo rating never fully resets: teams carry forward 60% of their rating gap from average, resetting the rest of the way toward a league-average baseline.
At its core, it's a standard Elo logistic model. Before each game, both teams' current ratings are converted into a win probability using a logistic curve. Every game moves a team's rating up or down based on the result, how surprising it was, and the margin of victory. Other factors also affect the size of the change, like home-court advantage, rest, and whether the game went to overtime.
Going back to the 1995–96 season, the TRACER Echo rating has correctly predicted the winner in 66.8% of games, with a Brier score of 0.209. After finishing the system, I tested it against the now-defunct NBA Elo ratings that used to be available on FiveThirtyEight. Echo beat the FiveThirtyEight model on accuracy, a result confirmed by significance testing.
TRACER was designed and built by me, TJ Sutton, during the downtime between graduation and starting grad school. I graduated from the University of Texas with a degree in Sport Management and a minor in sports analytics. The system came together as a learn-as-you-go process. I set out to teach myself about rating systems, which led me to Elo ratings in sports outside of chess. For the first four months, it only lived in Excel spreadsheets on my computer. In May, I decided to move it online to share with others. Hope you enjoy!
If you have any questions or feedback, you can reach me at tracersports4@gmail.com.