While I initially introduced my player rating, Estimated Impact, a while ago, I recently gave it a pretty extensive makeover and I’m generally pleased with results. My goal was basically to create a box score only metric that is a) more accurate and better at predicting future team performance than other box score metrics, and b) a very reasonable snapshot of present and historical player performance. Obviously, box-score only metrics have their noted limitations. And maybe more obviously, all-in one metrics are merely a two-dimensional picture of a three-dimensional world. But I’m confident that Estimated Impact does a good job at accomplishing my goals.
I don’t want to bore you with the details so I’ll keep it basic. This metric is based on a regression of certain box score elements against long term RAPM. For each season, I fit each player’s result to the team’s efficiency differential (this is usually a pretty small adjustment). I did the same with offense only and defense only, then fit off + def to total impact. For 1974-1977 I estimated turnovers by regression and used the same formula as I used in post-77 seasons. For pre-1974, I ran new regressions without any use of steals, blocks, etc. Needless to say, pre-74 estimates are probably less accurate. They’re certainly far from useless though, and they’re probably superior to any other measure of pre-74 production (e.g., WS/48 or PER).
In my own retrodiction testing, Estimated Impact outperforms every box score metric that I know of, and performs nearly as well as 2000s xRAPM (I’d welcome anyone to reproduce my results). And so I’m confident that it is currently the best all-in-one metric with respect to estimating historical production. For what it’s worth, the results also seem very reasonable to me. You can see all results from 1952-2013 here, or at the NBA & NCAA Stats page at the top right of the site. Or you can download the database here. Enjoy!