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Re: Home Team Assist Bias

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  • Mike G
    ... can t ... Yes. Home teams are granted 5.6% more assists in games they win. Home teams get 5.9% more assists in games they lose. I suppose it s possible
    Message 1 of 11 , Nov 3, 2003
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      --- In APBR_analysis@yahoogroups.com, "Dean Oliver" <deano@r...> > >
      > Ast/FGmade 02-03
      > > > .... Home Away
      > > > Win 62.4% 59.1%
      > > > Loss 61.2% 57.8%

      > 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?

      Yes.

      Home teams are granted 5.6% more assists in games they win.

      Home teams get 5.9% more assists in games they lose.

      I suppose it's possible that players are less selfish at home
      (wanting the fans to love them more?)
    • Michael Tamada
      ... From: Mike G [mailto:msg_53@hotmail.com] Sent: Sunday, November 02, 2003 3:29 PM ... All good points, although I would also take DeanO s point and drive it
      Message 2 of 11 , Nov 3, 2003
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        -----Original Message-----
        From: Mike G [mailto:msg_53@...]
        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
      • 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 3 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 4 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 5 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 6 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 7 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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