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1723Re: Cross Generational Simulating/Comparisons

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  • schtevie2003 <schtevie@hotmail.com>
    Jan 29, 2003
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      --- In APBR_analysis@yahoogroups.com, bchaikin@a... wrote:

      Bob:

      if you tired of the exchange of ideas concerning this discussion,
      once you have already made your position clear, but do not wish
      to be bothered to be asked to defend your postion with stats in a
      stats analysis group, then maybe this wasn't the forum for you to
      "...add a few pennies worth of thought on the issue of
      inter-temporal comparsions of NBA performance..."...

      Me Now:

      Actually, I don't tire of an exchange of ideas. Not in the least. All
      that I find tiresome is being obliged to repeat myself because
      you do not find it in your interest to respond to vexing arguments.
      And the only idea that has been imparted to me by your
      responses so far is that you have a vested interest in a "sim",
      and you want to use it in completely inappropriate ways, and it
      doesn't really matter what anyone says. Fair enough, I suppose;
      it's your toy, play with it as you will.

      This is not to say that none of your comments could be
      construed to have been offered in good faith. Specifically your
      request for data is perfectly reasonable. And I am happy to
      provide it. See below. But first repeating the punchline...

      *****************


      Me Before:

      the superiority of the average team in the early 80 to its 60s
      counterpart was on the order of 10 to 12 points per game (at a
      modern game pace). This is equivalent to how much better the
      best Bulls team was to the league average.

      Bob:

      not sure what these numbers mean or where they are coming
      from....how did you arrive at this or derive these numbers?...

      ...so let me get this straight, you are saying you have statistically
      come up with a way to show that if the average NBA team of the
      early 1980s (about 109 pts/g) played an average team from the
      1960s (115 pts/g) or early 1960s (almost 116 pts/g), the avg 80s
      team would beat the average 60s team, on average, by 10-12
      points, normalizing for modern times. the 95-96 bulls outscored
      their opponents that year by just over 12 pts/g. so you are saying
      the difference in ability to win of an average early 1980s NBA
      team versus/compared to an average 1960s or early 1960s is
      the same as the 95-96 bulls to the suns or hornets of 95-96
      (.500 teams that year)...

      is this correct?...

      Me Now:

      That is absolutely correct. More precise numbers below.

      ********************


      Me Before:

      The calculation I referred to was made by computing a measure
      of offensive (or equivalently defensive) productivity that I called
      "points per common possession" versus "common
      possessions per game". In the former case, the computation is
      average points scored in the numerator and average common
      possessions in the denominator. Common possessions are,
      by definition and construction, the same for both teams in a
      particular game (hence attractive for purposes of comparison
      and analysis) and are basically calculated by subtracting the
      number of offensive rebounds from the conventionally defined
      number of possessions a team enjoys in a game.

      Bob:

      fine...so fill in the blanks below so we can compare...or show us
      your numbers that show how you arrived at your result...

      pts/ sec/ pts/
      year FG% g poss poss
      5960 .410 115.3
      6061 .415 118.1
      6162 .426 118.8
      6263 .441 115.3
      6364 .433 111.0
      6465 .426 110.6
      6566 .433 115.5
      6667 .441 117.4
      6768 .446 116.6
      6869 .441 112.3
      6970 .460 116.7
      7071 .449 112.4
      7172 .455 110.2
      7273 .456 107.6
      7374 .459 105.7
      7475 .457 102.3
      7576 .458 104.3
      7677 .465 106.5

      pts/
      48min
      7778 .469 107.7 13.4 1.000
      7879 .485 109.8 13.5 1.029
      7980 .481 108.5 13.8 1.041
      8081 .486 107.5 14.0 1.043
      8182 .491 107.9 14.1 1.058
      8283 .485 107.9 13.8 1.037
      8384 .492 109.2 14.0 1.063
      8485 .491 110.2 13.9 1.066
      8586 .487 109.5 13.9 1.059
      8687 .480 109.2 14.1 1.067
      8788 .480 107.6 14.3 1.065
      8889 .477 108.5 14.1 1.062
      8990 .476 106.3 14.4 1.065
      9091 .474 105.5 14.5 1.063
      9192 .472 104.5 14.7 1.067
      9293 .473 104.5 14.7 1.066
      9394 .466 101.0 15.0 1.049
      9495 .466 100.6 15.3 1.069
      9596 .462 98.8 15.5 1.063
      9697 .455 96.2 15.8 1.053
      9798 .450 94.8 15.7 1.036
      9899 .437 90.9 16.0 1.009
      9900 .449 96.9 15.3 1.030
      0001 .443 94.0 15.6 1.020
      0102 .445 94.8 15.7 1.034

      DeanO has pointed out that "...this trend looks about right, even if
      my calculations have slight differences...". so if we are defining
      offensive productivity as pts/poss, i see similar pts/poss
      numbers with varying FG% and pts/g and game pace for 77-78
      thru today. if your number show a different trend for prior to
      77-78, lets see them...

      Me Now:

      Well, here are my numbers. They summarize the yearly average
      team performance in the league. There are four columns. The
      year refers to the end year of the season. "CP/game" is
      "Common Possessions per Game". "P/CP" is "Points per
      Common Possession". "P*/CP is the same stat except the
      points are modified to subtract out the third point of completed
      three pointers. Finally, "3pt effect" differences the two previous
      columns.

      Year CP/game P/CP P*/CP 3pt effect
      57 116.4 .856 .856
      58 124.7 .855 .855
      59 124.5 .870 .870
      60 131.2 .879 .879
      61 132.9 .889 .889
      62 131.4 .904 .904
      63 124.5 .926 .926
      64 121.5 .913 .913
      65 122.4 .904 .904
      66 126.1 .916 .916
      67 126.6 .927 .927
      68 124.8 .934 .934
      69 121.7 .923 .923
      70 122.0 .957 .957
      71 119.7 .939 .939
      72 116.4 .946 .946
      73 114.7 .938 .938
      74 111.7 .946 .946
      75 108.5 .946 .946
      76 109.6 .952 .952
      77 110.5 .964 .964
      78 111.0 .977 .977
      79 109.7 1.005 1.005
      80 107.3 1.019 1.012 .007
      81 105.9 1.021 1.016 .005
      82 104.7 1.037 1.031 .006
      83 107.0 1.015 1.010 .005
      84 105.7 1.042 1.036 .006
      85 106.1 1.045 1.036 .008
      86 106.2 1.038 1.029 .009
      87 105.0 1.047 1.034 .014
      88 103.5 1.045 1.030 .015
      89 104.9 1.041 1.021 .020
      90 102.4 1.045 1.024 .021
      91 102.0 1.043 1.020 .022
      92 100.7 1.046 1.021 .025
      93 100.7 1.045 1.015 .030
      94 98.7 1.028 .995 .033
      95 96.8 1.048 .991 .057*
      96 95.5 1.042 .980 .062*
      97 93.9 1.032 .967 .064*
      98 94.2 1.015 .968 .047
      99 92.7 .987 .939 .048
      00 96.7 1.008 .957 .050
      01 95.1 .997 .946 .051
      02 94.4 1.011 .956 .055

      Now before discussing trends and repeating the arguments, let
      me lay out the sources and methods behind these statistics.

      All data for the "NBA average" are from the Official NBA Guide.
      "CP/game" is the following sum of terms (divided by games
      played): Field Goal Attempts + 0.45 * Free Throw Attempts + 1.05
      * Turnovers - 1.045 * Offensive Rebounds. What this statistic
      represents again are the number of common possessions
      between a team and its opponent, or alternatively expressed, the
      number of continuous possessions - continuous meaning no
      additional possession is counted on an offensive rebound. Why
      the various factors. Possessions are disposed of as (1) field
      goal attempts, (2) two shot free throw attempts (three shot free
      throws are ignored) which I estimate as one half of 90% of all
      attempts (the other 10% being technicals and attempts after
      made shots) hence 0.45, (3) turnovers, where a 5% estimate of
      team turnovers is added, and (4) offensive rebounds, where
      4.5% is the estimate of team offensive rebounds. It should be
      noted that none of the results are sensitive to the factors chosen
      which is obvious as the last two terms effectively cancel
      eachother out.

      For the missing turnover and offensive rebound series prior to
      1974, I extrapolated using 1974 data. Specifically, for offensive
      rebounds, I calculated an offensive rebounding percentage for
      missed field goal attempts of 28.7 (and assumed a constant 5%
      value for offensive rebounds of missed final free throws). This
      should not be a controversial value as the percentage hovers
      quite closely about 30%. And for the turnover series, I assumed
      a stable relationship of turnovers to field goal attempts and two
      point field goal attempts, and this value in 1974 was 0.198. In
      this case, given the downward trend over time in turnover rate,
      this value is almost certainly biased low which would have the
      effect on the data of biasing CP/game down and P/CP up - that is
      to say exaccerbating the trends I identify.

      On to the analysis...

      What are the apparent trends. Well, I don't think there is any
      ambiguity on the point that the CP/game series trends
      downward over time. Given that I started off recalling data over
      the 60s and 70s, let me take '60 and '79 as endpoints to begin
      the discussion. Note a drop in game pace from 131.2 to 109.7
      possessions per game, a decrease of 15.6%. And during which
      time offensive productivity increased 11% (.879 to 1.005). Put
      another way, the average team in 1979, playing at its slower
      pace would be expected to beat the average team of 1960 by
      13.82 points per game (.126 P/CP * 109.7 CP/game).

      And how can this be said to be true? To repeat the argument
      that hasn't been adressed: slowing the pace of the game, all
      else equal, is only compatible theoretically with decreased
      offensive productivity. That there was an increase in offensive
      productivity must then mean that there was improvement in the
      way the game was played offensively. This didn't mean that the
      '79 players were supermen (though they may have been better
      athletes). It means that the offensive "technology" improved.
      And what were its intermediate effects: lower turnover rates
      (identified after '73) and higher field goal percentages (apparent
      throughout). It also doesn't rule the possibility that defenses
      improved also, just that on net there was a huge gain for the
      offenses.

      Now, Bob, if you can find another explanation for these offsetting
      trends, and frankly you must if you expect any serious
      consideration of results from "unadjusted" cross-generational
      simulations, please provide it. There may be one; I just haven't
      been able to come up with it over the years. Please try.

      As for the longer-term trends, picking up from the late seventies,
      the trends should be clear. The pace of the game continues to
      fall, and offensive productivity rises and plateaus for a few years
      in the middle 80s, then begins a "mild" decline (that if you hold
      the view that losing about four points per game is mild - roughly
      equivalent to home court advantage or, alternatively, half the way
      from mediocrity to championship status, as I noted before) or
      alternatively a very significant decline depending on your
      perspective.

      To understand this "dilemna" see the last two columns. They
      explain the contribution of the three point shot to maintaining
      "nominal" productivity. For example, in '02 three point shots
      raised the P/CP by 0.055 (or rougly 5 points per game). How
      P*/CP should be interpreted then is as a kind of low estimate of
      productivity. Clearly if teams would only be getting two points for
      a shot behind the three point line, they wouldn't take as many
      and would instead opt more for more mid-range jumpers.
      However, the low estimate might not be that far off. Consider
      that in '95 through '97 the three point distance was moved in to
      not much effect.

      Whatever the case, the essential is this. From the mid to late
      80's on, offensive productivity has trended downwards along with
      the pace of the game. In this environment, one could infer that
      either offenses were getting worse or that defenses were getting
      better. And my view is already on record. The argument again: if
      you have a quarter century of relentless net offensive progress
      (and almost certainly some counterveiling defensive progress
      as well) it seems absurd to argue that come the mid-80's
      progress came to a screeching halt and was followed by 15 to
      20 years of, yes, technological retrogression.

      So there is the evidence....gotta run...enjoy your dinner.
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