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Re: Home Team Assist Bias

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  • Dean Oliver
    Thanks, Mike, for clarifying what I had little time to explain. And, yes, Hakeem did have an assist taken away. They do review such things, though I don t
    Message 1 of 11 , Nov 3, 2003
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      Thanks, Mike, for clarifying what I had little time to explain. And,
      yes, Hakeem did have an assist taken away. They do review such
      things, though I don't know the full process.

      --- In APBR_analysis@yahoogroups.com, "Michael Tamada" <tamada@o...>
      wrote:
      > -----Original Message-----
      > From: Mike G [mailto:msg_53@h...]
      > Sent: Sunday, November 02, 2003 3:29 PM
      >
      >
      > --- In APBR_analysis@yahoogroups.com, igor eduardo küpfer
      > <igorkupfer@r...> wrote:
      > >> Has this been covered?
      > >>
      > >> Ast/FGmade 02-03
      > >>
      > >> Home Away
      > >> Win 62.4% 59.1%
      > >> Loss 61.2% 57.8%
      > >>
      > >> Seems like pretty clear bias against the visitors to me.
      > >
      > >Granting assists more liberally to the home team (almost 6% more
      > >generous, win or lose) might cause someone to think differently
      > >about a player -- unless they know of this bias.
      > >
      > >It's statistically significant, but it doesn't seem important,
      > >otherwise. Guys play half their games on the road, so there's no
      > >overall advantage.
      > >
      > >However, if someone points out that Jamal Crawford gets 5% more
      > >assists at home, and therefore he should play fewer minutes in
      road
      > >games, they are apparently mistaken. That's just par for the
      > >course: everyone gets 5-6% fewer assists on the road.
      >
      > All good points, although I would also take DeanO's point and
      > drive it even further: it's possible (unlikely, but possible)
      > that those stats reflect no bias at all, but instead are REAL.
      >
      > I.e. maybe visiting teams have fewer assists, percentage-wise,
      > than home teams. We know already that the visiting teams are
      > more likely to lose, and will score fewer points. Maybe they
      > rely more on one-on-one offense to score. Maybe they get
      > fewer fastbreaks and thus fewer chances for a Payton to pass
      > to a streaking Kobe for a layin.
      >
      > A similar statistic: I believe that researchers have already found
      > that home teams get more Free Throw Attempts, and are called for
      > fewer fouls, than visiting teams. Is that due to ref bias? Or is
      > it because the home teams literally are commiting fewer fouls?
      >
      > In the case of fouls, my guess is that most of the home-road
      > differential is caused by real differences and not ref bias.
      >
      > In the case of assists, I'd guess that home scorer bias is a strong
      > and quite possibly primary factor, but I don't think we have
      > evidence to come close to proving this.
      >
      > I'd have to think that the NBA has quality control measures for
      > its scorekeepers and statkeepers, and looks at video tapes to
      > see if assists are being awarded properly (didn't the NBA take
      > away a bogus home quadruple-double from Hakeem or someone like
      > that, after determining that the home statistician had been
      > over-generous in awarding assists -- or maybe it was even
      > a phantom rebound)? So the NBA probably does have true
      > comparative home and road stats. Whether it has found a
      > home-road difference, how large it is, and how much effort
      > the NBA is putting into eradicating it -- those are open
      > questions.
      >
      >
      > --MKT
    • igor eduardo küpfer
      ... From: Michael Tamada To: Sent: Monday, November 03, 2003 5:55 PM Subject: RE: [APBR_analysis] Re: Home
      Message 2 of 11 , Nov 3, 2003
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        ----- Original Message -----
        From: "Michael Tamada" <tamada@...>
        To: <APBR_analysis@yahoogroups.com>
        Sent: Monday, November 03, 2003 5:55 PM
        Subject: RE: [APBR_analysis] Re: Home Team Assist Bias

        <snip>

        >
        > All good points, although I would also take DeanO's point and
        > drive it even further: it's possible (unlikely, but possible)
        > that those stats reflect no bias at all, but instead are REAL.
        >
        > I.e. maybe visiting teams have fewer assists, percentage-wise,
        > than home teams. We know already that the visiting teams are
        > more likely to lose, and will score fewer points. Maybe they
        > rely more on one-on-one offense to score. Maybe they get
        > fewer fastbreaks and thus fewer chances for a Payton to pass
        > to a streaking Kobe for a layin.
        >

        I don't know. See the table here to see how different arenas have awarded
        assists to each team:

        http://members.rogers.com/strudel/deleteable/assists.htm

        Note that the numbers shown are how each team performed at that location
        relative to their season total performance, eg Atlanta was +2% at home while
        Chicago was -8% at Atlanta. 21 teams had higher assist totals at home, which
        seems only slightly odd. However, the fact that certain arenas show a lot of
        red ink makes me suspicious. While Chicago and Denver (among bad teams) and
        Philly and Boston (among better teams) were generous to their visiting
        opponents, Atlanta, Miami, Detroit and San Antonio were reluctant to hand
        out assists.

        I'm not sure what kind of connection these teams have.

        > A similar statistic: I believe that researchers have already found
        > that home teams get more Free Throw Attempts, and are called for
        > fewer fouls, than visiting teams. Is that due to ref bias? Or is
        > it because the home teams literally are commiting fewer fouls?
        >
        > In the case of fouls, my guess is that most of the home-road
        > differential is caused by real differences and not ref bias.
        >
        > In the case of assists, I'd guess that home scorer bias is a strong
        > and quite possibly primary factor, but I don't think we have
        > evidence to come close to proving this.
        >

        No. But I don't think it would be very difficult to establish home scorer
        bias, if it existed. I'll have a look at the numbers from previous seasons
        to see if a pattern exists in any of the arenas.


        ed
      • Dean Oliver
        ... awarded ... home while ... home, which ... a lot of ... teams) and ... hand ... And it s pretty hard to prove that this is anything but random noise in
        Message 3 of 11 , Nov 3, 2003
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          --- In APBR_analysis@yahoogroups.com, igor eduardo küpfer
          <igorkupfer@r...> wrote:
          >
          > ----- Original Message -----
          > From: "Michael Tamada" <tamada@o...>
          > To: <APBR_analysis@yahoogroups.com>
          > Sent: Monday, November 03, 2003 5:55 PM
          > Subject: RE: [APBR_analysis] Re: Home Team Assist Bias
          >
          > <snip>
          >
          > >
          > > All good points, although I would also take DeanO's point and
          > > drive it even further: it's possible (unlikely, but possible)
          > > that those stats reflect no bias at all, but instead are REAL.
          > >
          > > I.e. maybe visiting teams have fewer assists, percentage-wise,
          > > than home teams. We know already that the visiting teams are
          > > more likely to lose, and will score fewer points. Maybe they
          > > rely more on one-on-one offense to score. Maybe they get
          > > fewer fastbreaks and thus fewer chances for a Payton to pass
          > > to a streaking Kobe for a layin.
          > >
          >
          > I don't know. See the table here to see how different arenas have
          awarded
          > assists to each team:
          >
          > http://members.rogers.com/strudel/deleteable/assists.htm
          >
          > Note that the numbers shown are how each team performed at that location
          > relative to their season total performance, eg Atlanta was +2% at
          home while
          > Chicago was -8% at Atlanta. 21 teams had higher assist totals at
          home, which
          > seems only slightly odd. However, the fact that certain arenas show
          a lot of
          > red ink makes me suspicious. While Chicago and Denver (among bad
          teams) and
          > Philly and Boston (among better teams) were generous to their visiting
          > opponents, Atlanta, Miami, Detroit and San Antonio were reluctant to
          hand
          > out assists.
          >
          > I'm not sure what kind of connection these teams have.

          And it's pretty hard to prove that this is anything but random noise
          in addition to home teams playing better. I do finally see a little
          more of what you're getting at. Knowing something about how long
          certain guys have been on the job of stat-taking may help. My
          understanding is that guys usually under-record assists early on
          (having scored myself and being pretty stingy on assists, I heard that
          from a coach).

          >
          > > A similar statistic: I believe that researchers have already found
          > > that home teams get more Free Throw Attempts, and are called for
          > > fewer fouls, than visiting teams. Is that due to ref bias? Or is
          > > it because the home teams literally are commiting fewer fouls?
          > >
          > > In the case of fouls, my guess is that most of the home-road
          > > differential is caused by real differences and not ref bias.
          > >
          > > In the case of assists, I'd guess that home scorer bias is a strong
          > > and quite possibly primary factor, but I don't think we have
          > > evidence to come close to proving this.
          > >
          >
          > No. But I don't think it would be very difficult to establish home
          scorer
          > bias, if it existed. I'll have a look at the numbers from previous
          seasons
          > to see if a pattern exists in any of the arenas.
          >

          If we can establish it, it's a VERY significant issue. I did a number
          of evaluations of how much a biased ref changes the odds of winning.

          Hmm

          DeanO
        • John Hollinger
          I actually covered this briefly in the Prospectus. Memphis scorekeeper gave him assists like it was Halloween candy. ... at
          Message 4 of 11 , Nov 4, 2003
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            I actually covered this briefly in the Prospectus. Memphis'
            scorekeeper gave him assists like it was Halloween candy.




            --- In APBR_analysis@yahoogroups.com, "harlanzo" <harlanzo@y...>
            wrote:
            > --- In APBR_analysis@yahoogroups.com, "Dean Oliver" <deano@r...>
            > > My take on home court bias in reffing or scoring is this: you
            > can't
            > > tell whether it's home court bias or just players playing better
            at
            > > home. Is there any way to really distinguish between these?
            > >
            > > DeanO
            >
            > I'd be interested to see how the white Jason Williams home assists
            > changed when he went from Sacramento to Memphis. It was rumored
            > that Memphis' official scorer was exceedingly generous.
          • John Hollinger
            They did the same thing to Webber last year after the Sac scorekeeper gave him a bogus assist to get a triple-double. ... And, ... ... no ...
            Message 5 of 11 , Nov 4, 2003
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              They did the same thing to Webber last year after the Sac scorekeeper
              gave him a bogus assist to get a triple-double.



              --- In APBR_analysis@yahoogroups.com, "Dean Oliver" <deano@r...>
              wrote:
              >
              > Thanks, Mike, for clarifying what I had little time to explain.
              And,
              > yes, Hakeem did have an assist taken away. They do review such
              > things, though I don't know the full process.
              >
              > --- In APBR_analysis@yahoogroups.com, "Michael Tamada"
              <tamada@o...>
              > wrote:
              > > -----Original Message-----
              > > From: Mike G [mailto:msg_53@h...]
              > > Sent: Sunday, November 02, 2003 3:29 PM
              > >
              > >
              > > --- In APBR_analysis@yahoogroups.com, igor eduardo küpfer
              > > <igorkupfer@r...> wrote:
              > > >> Has this been covered?
              > > >>
              > > >> Ast/FGmade 02-03
              > > >>
              > > >> Home Away
              > > >> Win 62.4% 59.1%
              > > >> Loss 61.2% 57.8%
              > > >>
              > > >> Seems like pretty clear bias against the visitors to me.
              > > >
              > > >Granting assists more liberally to the home team (almost 6% more
              > > >generous, win or lose) might cause someone to think differently
              > > >about a player -- unless they know of this bias.
              > > >
              > > >It's statistically significant, but it doesn't seem important,
              > > >otherwise. Guys play half their games on the road, so there's
              no
              > > >overall advantage.
              > > >
              > > >However, if someone points out that Jamal Crawford gets 5% more
              > > >assists at home, and therefore he should play fewer minutes in
              > road
              > > >games, they are apparently mistaken. That's just par for the
              > > >course: everyone gets 5-6% fewer assists on the road.
              > >
              > > All good points, although I would also take DeanO's point and
              > > drive it even further: it's possible (unlikely, but possible)
              > > that those stats reflect no bias at all, but instead are REAL.
              > >
              > > I.e. maybe visiting teams have fewer assists, percentage-wise,
              > > than home teams. We know already that the visiting teams are
              > > more likely to lose, and will score fewer points. Maybe they
              > > rely more on one-on-one offense to score. Maybe they get
              > > fewer fastbreaks and thus fewer chances for a Payton to pass
              > > to a streaking Kobe for a layin.
              > >
              > > A similar statistic: I believe that researchers have already
              found
              > > that home teams get more Free Throw Attempts, and are called for
              > > fewer fouls, than visiting teams. Is that due to ref bias? Or is
              > > it because the home teams literally are commiting fewer fouls?
              > >
              > > In the case of fouls, my guess is that most of the home-road
              > > differential is caused by real differences and not ref bias.
              > >
              > > In the case of assists, I'd guess that home scorer bias is a
              strong
              > > and quite possibly primary factor, but I don't think we have
              > > evidence to come close to proving this.
              > >
              > > I'd have to think that the NBA has quality control measures for
              > > its scorekeepers and statkeepers, and looks at video tapes to
              > > see if assists are being awarded properly (didn't the NBA take
              > > away a bogus home quadruple-double from Hakeem or someone like
              > > that, after determining that the home statistician had been
              > > over-generous in awarding assists -- or maybe it was even
              > > a phantom rebound)? So the NBA probably does have true
              > > comparative home and road stats. Whether it has found a
              > > home-road difference, how large it is, and how much effort
              > > the NBA is putting into eradicating it -- those are open
              > > questions.
              > >
              > >
              > > --MKT
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