I take (and was aware of) the point that plausible alterations of the MPG variable value in the ASPM regression (or "new" RAPM prior) wouldn't make a tremendous difference in the resulting estimates for any given player (though I have the distinct impression that AI is relatively favored by the specification of the regression in Daniel's work, given the nature of how he filled up the stat sheet) and a notional adjustment of a fraction of a point per 100 possessions isn't going to significantly reshuffle any given player's HOF rank.
The underlying issue (relating to the topic of this thread) though is what approach to rating
individual players, in particular elite players (because, let's be honest, by our conversations, it is revealed that nobody cares about notionally non-elite players) is more likely to offer "true" results. Is it
necessarily estimates based on a system that best explains overall variation? I don't think such a claim can be supported.
I neglected to reply to this remark:
permaximum wrote:You didn't have any problem with an invalid (but reliable) metric such as WS or too noisy RAPM aka "Nick Collison metric" "Amir Johnson metric" goes on an on.
but will now, as it is on point, and I should have said that this couldn't be a more complete misrepresentation of my views (as expressed in this forum).
A case in point. I believe I was the first person to express dissatisfaction with one particular and conspicuous aspect of initial RAPM results. The tremendous improvement in explanatory power? Great! You want to use this instead of APM to retro/pre-dict team results? But of course. The implication, however, that the greatest player seasons were no longer about +10 and a bit above (as suggested by multi-year APM) but only contributed, as I recall, less than half that? Not so great!
Then came the first round (I think I'm getting the history right) of xRAPM. Tremendous improvement! The yearly (+/-) data could speak for itself with only relatively minor intervention (the box-score prior) and for the topic at hand (the relative contributions of the elite as a whole) a bit of sanity was restored.
And then came successive amendments of xRAPM; I think I count three. Modifications for: the observed fact that players player harder when behind and slack off when ahead, aging effects, and coaching effects. In terms of generally improving the regression results, there is no doubt. In terms of improving the valuation of the NBA elite, a mixed bag, but I suspect an overall step for the better.
Might the generally observed "countercyclical effort" not describe the league's best players? Perhaps that is one factor that tends to make the great great? Whatever the case, as I recall, the effect wasn't that large anyway. Adding the aging curve? Again, kind of revealed to be small potatoes, but unquestionably a step in the right direction, as no player can escape time. Modifying player estimates to take into account notional effects of coaching impact? In theory, a very good idea, but, in practice, I don't think the +/- data are able to speak correctly. Do the coaching estimates provided improve the explanatory power of the regression? Yes. Do they improve our perception of the relative value of the NBA elite? Poor Kevin Durant.
So, to summarize, the question is this: If one is interested in the performance of a particular player, an elite player, for whom there are years and years of data of thousands and thousands of possessions, and one is generally persuaded as to the superiority of +/- approaches (as any right-thinking person should be) why would one not prioritize estimates that are directly (and serially) informed by these actual on-court contributions rather than a synthetic approximation, based on box-score regression, no matter if "on average" it proves better league-wide?