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3693Re: Dampier (was Article from _The Economist_)

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  • Mike G
    Apr 7, 2004
      --- In APBR_analysis@yahoogroups.com, "Michael Tamada" <tamada@o...>
      wrote:
      ..
      > if we're looking at a 29 year old Dampier or whoever, and trying
      to predict
      > what his age 30, 31, etc. stats will look like, then we don't want
      to look
      > at the overall average for 30-year olds (or 30-year old all-
      NBAers, or
      > whatever group). Instead we'd want to look at what the typical
      *change
      > in performance* is for a 30-year old, compared to what he did as a
      29-year
      > old.

      It so happens I've been doing something like this.

      I also corrected for what might be considered a "bias" in a manley-
      type production figure: the NBA has overall been
      losing "productivity", on a per-game basis. Thus, all 30-year-olds
      have been around long enough to see a significant decrease in
      production, among all players.

      My figures show a per-game/per-team high around 144 in the mid-'80s,
      which has since dropped to about 125. Not sure of the manley
      formula Ed used, but I'm applying one equally to teams and
      individuals; using a formula like the one BobC layed out.

      Briefly, I see an average change based on age that looks like this:

      %inc is average increase (decrease if negative) of the age group
      that went on to play the next year, in "manley credits".

      SS# is sample size (player-seasons since 1978)

      age %inc SS#
      18 .897 3
      19 .332 12
      20 .353 30
      21 .130 94
      22 .224 360
      23 .113 729
      24 .044 771
      25 -.011 734
      26 -.020 700
      27 -.065 625
      28 -.071 562
      29 -.094 519
      30 -.129 453
      31 -.171 374
      32 -.125 274
      33 -.181 203
      34 -.183 142
      35 -.178 91
      36 -.246 62
      37 -.319 36
      38 -.236 20
      39 -.026 8
      40 -.246 3
      41 -.271 2
      42 -.604 1

      For 519 players age 29 who went on to play in their 30th year, an
      average loss of 9.4% has occurred.

      Earlier studies have shown an erosion of minutes, on average, from
      year to year in a player's career. No doubt, this is a part
      contributor in the total production a player loses. I'll be back
      with per-minute losses due to aging.
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