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Home Team Assist Bias

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  • igor eduardo küpfer
    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. ed
    Message 1 of 11 , Nov 2, 2003
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      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.

      ed
    • Mike G
      ... 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
      Message 2 of 11 , Nov 2, 2003
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        --- 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.
      • Dean Oliver
        ... 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
        Message 3 of 11 , Nov 2, 2003
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          --- In APBR_analysis@yahoogroups.com, "Mike G" <msg_53@h...> wrote:
          > --- 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.

          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
        • harlanzo
          ... can t ... 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
          Message 4 of 11 , Nov 2, 2003
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            --- 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.
          • 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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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