DSMok1 wrote:I ran a full era adjustment for everything, which helps the 1960s and 1980s and hurts the 1970s and particularly the ABA. Here's the adjustment chart:
It's very interesting. This looks at all players near their peak that played in both seasons, and sees whether they perform better in the first or second season, adjusted for aging. Statistically, there is a fair amount of error possible, not in the overall shape of the adjustment curve, but in the overall slope--in other words, it is quite possible the left end of the line should be moved up or down a point or two do to some slight systematic bias. So take it with a grain of salt.
Hopefully a productive conversation can be had about this very interesting graph (perhaps it even merits being split away from this thread because the issue of all-time ranking of players is but derivative).
My initial reaction to seeing this story told (including the title!) is that there seems to be big problems with it (or at least questions) and further consideration reinforces that impression.
What is or ought to be our common, a priori view about "era adjustments"? Well, first, the term itself should be considered something of an imprecision. What should determine changes in the average quality of league play across time? In expectation, there is but one general factor: talent dilution/concentration. And here the sole, general determinant is the tension between league expansion and demography, writ large. Then overlaying this is a stochastic element, where incoming and outgoing cohorts in any given year have certain random, quality variation, e.g. not every year does a LeBron enter the league.
So, in essence, there ought to be no real "eras" to speak of; instead, there is the overlay of the historical schedule of league expansion/contraction (within and without the NBA) and relevant demographic trends (growth rates in player population subsets) what in turn are influenced by economic and social factors.
As to the former, there is the relative, economic attractiveness of supplying labor as a player in the NBA vs. all other avocations (athletic and non). And here this has risen markedly over time. Then as to the latter, the most important factors have been the unwinding the malign effects of past discrimination against African-Americans then later in time against "Euros".
Given this general analytic structure (which we all agree upon...right?) what are the implications about what we would expect an "era adjustment" plot to look like, generally?
Well, replying to what Daniel says is a shortcoming of his presentation (taking the present day as a baseline) there is the issue of the "vertical adjustment" for the initial year (1952 in his plot?) And if one admits any reasonable lack of opportunity for African-Americans beginning in what was the end of the Jim Crow era, that one-off adjustment will be way down (a direction reinforced by all other relevant factors, by the way). And then there would be catch-up over time according to some rule, until the present racial/non-US native composition was achieved. (And a similar approach would be taken for the influx of non-native US players.) But I will leave the discussion of such particulars for now, but we can discuss details if there is any desire to.
Then overlaying such a relatively smooth demographic plot we would expect to see discontinuities for realized league expansions and contractions (what we can infer from Daniels' chart as well). As for the expected size of the jumps, these can probably be reasonably estimated for their average expected effect based upon the contemporaneous distribution of plus-minus data. (Again, a discussion of particulars can be undertaken should there be interest.)
And that should be about it, what suggests a very different time path of "era adjustment" than revealed by Daniels' plot.
Let me discuss one "era" in question that particularly raises my suspicions: the twenty year, near monotonic and linear decline from the peak of 1983-84 to trough in 2003-04. Why this raises special concern is that I suspect that all demographic/expansion issues probably not just cancel themselves out, but imply what should have been a net talent concentration.
(By this I mean that if you total the minutes or Win Shares taken by non-native US players in 2004 and account for the general US population growth over time, league expansion was running behind the relevant population growth - and I assume that by 1984 the racial representation issues were essentially off the table...but perhaps not. And, of course, in terms of economic opportunity for athletes, the NBA was increasingly the best place to be.)
But instead we learn from the exhibited plot that this was a period of dramatic, really dramatic, and relentless deterioration in what I am interpreting is the quality of the average NBA player. And the story for this is what exactly? It cannot be randomness can it, in the sense that it just so happened that for about twenty consecutive years inferior classes of athletes just happened to enter the NBA?
My suspicion, and I don't understand enough of the method used to really comment, is that what the plot is picking up is a period of exogenous improvements in defense that diffuse league-wide over time - at least that is a story consistent with my understanding of the historiography. Specifically, as the story goes, the end of the 80s coincides with Pistons' efforts to slow down Michael Jordan, followed by Pat Riley's influential interpretation and generalization of the same philosophy. We all remember the introduction of the "no layups" rule, right? And then there was the "mini-era" of the shortening of the 3-point line that ironically reinforced these same defensive tendencies.
And as goes this two decade "era" there are similar problems throughout. Daniel writes that errors aren't possible in the overall shape of the adjustment curve, and though I am loathe to question his judgment, I would like at least for there to be some story offered for these "unrandom" results. Might breaking down the plot in terms of offense and defense possibly clarify matters?
