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RE: [APBR_analysis] Re: Home Team Assist Bias

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  • 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 1 of 11 , Nov 3, 2003
      -----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 2 of 11 , Nov 3, 2003
        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 3 of 11 , Nov 3, 2003
          ----- 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 4 of 11 , Nov 3, 2003
            --- 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 5 of 11 , Nov 4, 2003
              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 6 of 11 , Nov 4, 2003
                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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