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Re: Tendex rating

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  • Dean Oliver
    ... calculate ... Model analysis can be evaluated on 3 (or 4) philosophies: 1. Simplicity 2. Reality 3. Conservatism (4. Consistency) Every model that we
    Message 1 of 6 , Nov 2, 2001
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      --- In APBR_analysis@y..., "Mike Goodman" <msg_53@h...> wrote:
      > >many people have tried to come up with a single number that
      > > measures overall player ability, and i feel this rating is the
      > closest to
      > > doing just that - while also still being simple enough to
      calculate
      > (so any
      > > fan can do it) and by using all of the stats that are readily
      > available to
      > > fans.
      >
      > That is also a criterion of mine. Using traditional, recorded
      > quantities not only makes for universal availability, it minimizes
      > the number of columns necessary in a player's statistical profile.
      >

      Model analysis can be evaluated on 3 (or 4) philosophies:

      1. Simplicity
      2. Reality
      3. Conservatism
      (4. Consistency)

      Every model that we use is based upon a compromise between #1 and
      #2. My favorite example is that people used to think that orbital
      physics was all built on circles. The sun went around the earth in a
      big circle. If it wasn't just a circle, it was circles within
      circles. There was a good name for all of this that fails me right
      now and I know someone out there can spell this out better. People
      tried to model what they saw in the sky based on circular orbits or
      circular orbits within circular orbits. It fit the data pretty well,
      but it got damn complicated. Some dude -- I think it was Kepler --
      came up with the laws of orbital motion that had ellipses. These
      ellipses, after the initial period, where, ohmigod Those aren't as
      easy to use as circles!!! -- people realized that they were much more
      robust, explaining things in a way that was ultimately simpler. Then
      (I feel horrible for not remembering this stuff better), we got
      gravity and gravity predicted the elliptical orbits. We got real!
      It all fit together. A model that was not as simple at the start as
      big circles, but ultimately explained a lot more fairly simply.

      What's the 3rd thing? Well, conservativeness is important when using
      a model to set policy (something I do at work). Say you're
      interested in only the good defensive players in the league (for some
      reason) and you want your stat to get those guys. Well, you want to
      make sure you don't get the mediocre ones. Your statistic should
      come out and there should be no argument that the method you chose is
      only going to get good defensive players. Not sure it matters much
      for basketball, except if you're helping the league to rewrite rules.

      I frankly hate the 4th one. A lot of times, someone has done
      something stupid before, but because of "consistency", we have to do
      the same stupid thing again.

      My point, which is probably lost through all that rhetoric, is that
      Tendex is simple, but may not be realistic. whatever realistic is.
      Tendex has nothing it can be compared to in order to say if it's
      realistic. It is only a rating. It reflects not points scored nor
      allowed. If it reflects production, no one knows how to ground truth
      it. Tendex and the like are just numerical values reflecting
      approximate ratings. They work pretty well in doing trade value.
      GMs seem to qualitatively use them when doing trades or signing
      players. We generally don't see too many trades of high "production"
      players for low "production" players (except in sign-and-trade deals
      now). People get burned a lot relying on tendex, of course. Vin
      Baker was never ever worth what Seattle paid for him, yet his Tendex
      was quite high. Antawn Jamison is another with a high Tendex (and,
      now, a high salary), but no established effectiveness for winning
      and, more and more, a history that suggests his future won't be too
      great. But the "simplest" model says that he's pretty good.

      The other thing I'd say is what Bill James always said -- most of the
      time you're doing an analysis, you don't care about overall quality,
      you care about one specific thing. Can they rebound? Can they
      score? Can they play defense? Do their skills fit our needs?

      > > for those thinking david robinson is over the hill, the spurs led
      > > the league in wins last year not just because of duncan (.592
      > tendex/min -
      > > 5th best in the league) but also because of the admiral (.573 -
      8th
      > best in
      > > the league despite scoring just 14 pts/g) - two players in the
      same
      > starting
      > > lineup with 2 of the top 8 tendex/min ratings in the league...
      > >
      > > bob chaikin
      > > bchaikin@b...
      >
      > Admiral ranked #13 in my hybridized per-game/per-minute rankings.
      > This is lower than the per-minute rank, and higher than the per-
      game
      > rating.
      > What makes David over-the-hill is that he cannot produce at that
      high
      > rate for as many minutes as before. (Note, I said over-the-hill,
      not
      > washed-up.)

      Hmm, one of the more controversial subjects here, I think, is the
      Admiral. I heard more complaints about him being in the NBA Top 50
      than about anyone else. No killer instinct, they said. Not a
      champion, they said. But the numbers have been great. He didn't
      have the supporting cast. Once he got a supporting cast, that cast
      was Duncan and who supported who?

      How has the Admiral performed in the playoffs relative to the regular
      season, then relative to other people? Has he fallen off much more
      than others in the playoffs? He looked absolutely horrible vs. the
      Lakers last year.

      Mike -- this statement:

      > What makes David over-the-hill is that he cannot produce at that
      high
      > rate for as many minutes as before.

      The implication is that people can be as good, as efficient as they
      get older, but just not as long. Was his "rate" (per minute) as high
      before as it is now? Any sense for how this goes down with age
      relative to minutes played?

      Dean Oliver
      Journal of Basketball Studies
    • Michael K. Tamada
      ... [...] ... I think the word you re looking for is epicycles . Unless you re looking for the more general term of adding more and more little adjustments
      Message 2 of 6 , Nov 3, 2001
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        On Fri, 2 Nov 2001, Dean Oliver wrote:

        > Model analysis can be evaluated on 3 (or 4) philosophies:
        >
        > 1. Simplicity
        > 2. Reality
        > 3. Conservatism
        > (4. Consistency)

        [...]

        >#2. My favorite example is that people used to think that orbital
        >physics was all built on circles. The sun went around the earth in a
        >big circle. If it wasn't just a circle, it was circles within
        >circles. There was a good name for all of this that fails me right
        >now and I know someone out there can spell this out better. People

        I think the word you're looking for is "epicycles". Unless you're looking
        for the more general term of "adding more and more little adjustments to
        the model to make it fit reality, so much so that the model starts falling
        apart under its own complexity". Thomas Kuhn (referred to in Stuart
        McKibbin's posting) might've had a word for this too, but I forget. When
        the old model gets pushed aside by a new different one, that's a "paradigm
        shift".

        Hey didn't you go to Caltech and shouldn't you know this stuff? ;) But
        you did nail the correct answer to the ellipse modeller: Kepler.

        [...]

        > What's the 3rd thing? Well, conservativeness is important when using
        > a model to set policy (something I do at work). Say you're
        > interested in only the good defensive players in the league (for some
        > reason) and you want your stat to get those guys. Well, you want to
        > make sure you don't get the mediocre ones. Your statistic should
        > come out and there should be no argument that the method you chose is
        > only going to get good defensive players. Not sure it matters much
        > for basketball, except if you're helping the league to rewrite rules.

        I'm not sure about this one. Because an overly "conservative" list of
        good defensive players will STILL get arguments -- from people who
        complain that the list left out players X, Y, and Z, who are great
        defenders.

        It's analogous to statistics: you can be "conservative" and minimize the
        probability of a Type I error by choosing a small significance level. But
        in doing so, you are automatically raising the probability of a Type II
        error.

        A list of "great defenders" which is conservative will avoid Type I
        errors, but will be making more Type II errors.

        Decision theory tells us we should look at the relative cost of Type I
        errors and Type II errors and choose a signficance level which balances
        out the likely errors so as to minimize the costs.

        In other words, sometimes we want a "conservative" list of great
        defenders, but other times a not so conservative one. Depending on the
        purpose of the list.

        > I frankly hate the 4th one. A lot of times, someone has done
        > something stupid before, but because of "consistency", we have to do
        > the same stupid thing again.

        Well there's another kind of consistency, one which is a good thing to
        have: logical self-consistency. E.g. rating systems should avoid
        double-counting (unless there is a reason to put a heavy weight on that
        variable).


        --MKT
      • Mike Goodman
        ... David Robinson is probably a great person, as well as a colossal figure in the history of the game. But: He left a clue to his attitude in an interview I
        Message 3 of 6 , Nov 3, 2001
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          --- In APBR_analysis@y..., "Dean Oliver" <deano@t...> wrote:
          .........
          > Hmm, one of the more controversial subjects here, I think, is the
          > Admiral. I heard more complaints about him being in the NBA Top 50
          > than about anyone else. No killer instinct, they said.
          >

          David Robinson is probably a great person, as well as a colossal
          figure in the history of the game.
          But:
          He left a clue to his attitude in an interview I saw some years ago.
          Invoking his Christian ideals, he said his faith in God elevates his
          game; and that (quoting from memory) "when going up against an
          Olajuwon or a Robert Horry, I feel like David against Goliath..."
          Eh?
          In other words, he doesn't feel physically superior to Robert Horry?

          > How has the Admiral performed in the playoffs relative to the
          regular
          > season, then relative to other people? Has he fallen off much more
          > than others in the playoffs? .......


          Per-36-minute standardized equivalents for David Robinson, career

          Games Min. Pct. Sco. Reb. Ast PF Stl TO Blk Total
          Regular 845 35.8 .570 26.5 11.7 2.8 3.1 1.5 2.7 3.3 45.7
          Playoff 96 37.5 .532 22.8 12.2 2.8 3.4 1.4 2.6 2.9 41.8

          The ratio of this playoff rate to regular season rate is .915.
          The "average" playoff rate is around .940 (for 515 alltime players).

          > Mike -- this statement:
          >
          > > What makes David over-the-hill is that he cannot produce at that
          > high
          > > rate for as many minutes as before.
          >
          > The implication is that people can be as good, as efficient as they
          > get older, but just not as long. Was his "rate" (per minute) as
          high
          > before as it is now? Any sense for how this goes down with age
          > relative to minutes played?
          >
          > Dean Oliver
          > Journal of Basketball Studies

          It depends on the player, the team situation, and the coach. Popovich
          may be "babying" DRob by using him only 30 mpg, but it has been
          several years now since he has had back problems and other ailments.
          Jordan seems willing to go 40 minutes at age 38, but that is just
          another chapter-in-the-making of a unique case.
          Per-minute rates are down for any player past his prime. The more
          involved issue is : how to get the most production. Over the course
          of a whole season (playoffs particularly), and over the course of a
          career.
        • Dean Oliver
          ... stuff? ;) But ... Hey, going to Caltech means I know the formulas, how to derive them from first principles, what all the little math symbols mean, and
          Message 4 of 6 , Nov 3, 2001
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            --- In APBR_analysis@y..., "Michael K. Tamada" <tamada@o...> wrote:
            >
            > Hey didn't you go to Caltech and shouldn't you know this
            stuff? ;) But
            > you did nail the correct answer to the ellipse modeller: Kepler.
            >

            Hey, going to Caltech means I know the formulas, how to derive them
            from first principles, what all the little math symbols mean, and how
            to go 40 hours without sleeping. It doesn't mean I know the names of
            the famous dead guys. Heck, by going to Caltech, I have a right to
            forget names.

            >
            > I'm not sure about this one. Because an overly "conservative" list
            of
            > good defensive players will STILL get arguments -- from people who
            > complain that the list left out players X, Y, and Z, who are great
            > defenders.
            >
            > It's analogous to statistics: you can be "conservative" and
            minimize the
            > probability of a Type I error by choosing a small significance
            level. But
            > in doing so, you are automatically raising the probability of a
            Type II
            > error.
            >

            This is pretty much my point. In policy making, a policy maker
            really wants to reduce one of those types of errors. Usually the
            policy makers don't care about the cost-benefit of Type I vs. Type II
            errors. Their job is minimize one type and fight with everyone else
            who wants to minimize the other type.

            Not sure how that relates to any hoops stuff we're doing right now,
            but it might in the future, when we start using all those funky math
            symbols.

            > Well there's another kind of consistency, one which is a good thing
            to
            > have: logical self-consistency. E.g. rating systems should avoid
            > double-counting (unless there is a reason to put a heavy weight on
            that
            > variable).

            That's true and a good . I can add that to the routine speech I give
            at work. Then when my people look at me funny, I can blame it on you.

            I would phrase what you're talking about a little differently here,
            though. A method makes assumptions at the start and those
            assumptions should remain true at the end. Thinking off the top of
            my head -- if Tendex assumes all those things to be worth one point,
            shouldn't they all be worth one point at the end, too? Does this
            mean Tendex should add up to points scored?

            I know all the arguments pro and con with Tendex. I always point out
            that Tendex, when applied to teams has only about a 70-80%
            correlation with winning percentage. Which means it's not terribly
            reliable for predicting winning teams and probably no more reliable
            for predicting winning players. I also don't like the fact that it
            really just encourages a lot of shooting. I don't know how well
            Tendex correlates with points scored. But unlike baseball, where
            position players are pretty much responsible for offense and pitchers
            for defense, basketball players are responsible for both. That's why
            I try to keep offensive and defensive contributions separate for
            individuals. Doug Steele has an offensive and defensive Tendex
            rating based on some conversations we had in '94. It was a start.

            DeanO
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