OhayoKD wrote:lessthanjake wrote:OhayoKD wrote:
A season's worth of games is nowhere near enough to stabilize and as has been noted, applying a similar sampling distributions and process for other players with full rapm out led to big jumps. When we have similar data for everyone, this becomes useful. Right now it's not.
I think you may be conflating concepts here a bit. A season’s worth of games is definitely not enough to “stabilize” RAPM for purposes of minimizing random variance. But we aren’t talking about random variance. We’re talking about how long it takes for it to stabilize in terms of moving a player’s RAPM from the 0 prior to the general vicinity of where they belong. That’s not about random variance at all—quite the opposite actually. It’s a fundamentally different concept.
And a single season’s worth of data is a pretty good amount for these purposes. If it wasn’t then we’d expect the top pure RAPM numbers in a given year to be consistently higher as we expand out the number of years being analyzed. And we don’t really see that. Take, for instance this website, which is pure RAPM (without any priors, just like Squared’s RAPM) that conveniently allows us to filter the top players by one-year, three-year, and five-year RAPM: https://thebasketballdatabase.com/2016-17RegularSeasonPlayerRAPMComprehensive.html. Obviously the exact details will depend on the year we look at and there’s random variance at play here, but if you peruse the years you’ll find that the top values for one-year RAPM are generally very similar to the top values for three-year and five-year RAPM.
Of the top 10 in your site, 7 see at least a >1 point drop from 1-year to 5 year and 3 see a >2 point drop. (2 see <.5 increases). These results look pretty different from 1 year to 5 year and those are full samples where it's available for everyone.
This is a really curious post, since your argument is that RAPM goes substantially *up* as the sample gets larger than one year, and here you’re pointing to the fact that a bunch of peoples’ RAPM values went *down* as the sample got larger than one year. I think you got yourself confused here, and argued against your own point.
I’ll note that we see similar things in others years too. For instance, to take an adjacent year: https://thebasketballdatabase.com/2015-16RegularSeasonPlayerRAPMComprehensive.html. Even if you filter it for the top five-year RAPMs (so we’re not ending up accidentally cherry-picking positive random variance in the one-year data), 7 of the top 10 had higher one-year RAPMs. That said, having briefly perused other years before I made my prior post, I think there’s years where it goes the other way (random variance is at play here, so we’d expect that), which is why I conservatively said the values “are generally very similar” rather than making any actual directional assertion. Ultimately, the point is merely that we do not see the longer timespans be consistently far higher—and we’d need to see them be consistently higher if one year was nowhere near large enough for pure RAPM to stabilize for these purposes (and Hakeem needs that to be the case given how much higher Jordan’s Squared RAPM is). You arguing that these RAPM values get notably *lower* as the sample gets larger definitely strongly suggests RAPM in longer timespans are not consistently far higher than one-year RAPM!