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<p>Geoff:</p>
<p>Thanks.</p>
<p><b>Supergroup</b><br>
</p>
<p>First of all, I agree with you about the supergroup. Indeed many
years ago I put forward the view that, having set the bar, the
starting strength of those above the bar should represent their <b>average</b>
strength not simply "bar+1".</p>
<p>Thus, for example, if the entry is 3d 3d 2d 1d 1k 1k in a 3 round
tournament then the bar should be at 1d but those above the bar
should start at +1 (if the 1 kyus start at -1), and not 0. I ran a
few tournaments on this basis probably 15 - 20 years ago, but I
was told I was wrong and the idea never really caught on.</p>
<p><b>Spreadsheet Comments</b><br>
</p>
<p>When I look at your spreadsheet, there are 4 tournaments where
the number above the bar is less than the number recommended in
the Table. Of these:-</p>
<p>a) I don't understand No. 12 (4d, 5*1d) where the bar was at 1d
but there was only 1 player above the bar. The correct answer is
for the bar to be at 1 dan with 6 above the bar</p>
<p>b) Nos 16 and 19: why did the 1k not play both 3k in No 16? Were
handicaps used in No 19? Both cases are difficult , and there
might be a case for handicaps (consult the players?)<br>
</p>
<p>c) No 25 The bar should have been at 1k with a supergroup.<br>
</p>
<p>No 1 should have had the bar at 1 dan , when the depth would have
been 3. <br>
</p>
<p>In addition, No 13 should be a supergroup (see above) with the
bar at 1d</p>
<p> Finally, of course, Nos 7 and 21 have too many above the bar.
For No 7, I would have put the bar at 1 dan, No 21 is difficult
and a fudge may be required.</p>
<p><b>Use of Organiser's Handbook Tables</b></p>
<p>You state:- <br>
</p>
<p><i>There is plenty of evidence to show that you cannot set the
bar based on the number of rounds alone. For a 6 round
tournament, the BGA tables advise you to have a population range
from 7 to 15 players, and in some tournaments that would lead to
a range from 5k to 2d or worse</i>.</p>
<p>Sorry, I am confused: I don't see this evidence. In a 6 round
tournament the ultimate winner will (ideally) end up playing
people ranked 2nd to 7th, and this will be the case irrespective
of where the bar is placed. And the winner's oppponents should all
have a chance of winning the Tournament: imagine the outcry if a
maverick player gets 6/6, but one of the people that he beat is
said to have won the tournament. (This would have happened last
year at the 3 peaks if James Richards had beaten me in the last
round, see <a class="moz-txt-link-freetext" href="http://www.britgo.org/results/2017/threepeaks">http://www.britgo.org/results/2017/threepeaks</a>).</p>
<p>I reiterate my stance that the Table should take priority, and
that if there is a choice of values within this range then bar
depth is an important consideration.</p>
<p>Perhaps I should shut up and let others comment.<br>
</p>
<p>Toby.<br>
</p>
<br>
<div class="moz-cite-prefix">On 08/11/2018 14:28, Geoff Kaniuk via
tournament-org wrote:<br>
</div>
<blockquote type="cite"
cite="mid:07a1a51c-b2ae-6223-1c92-bf74f43f61fe@kaniuk.co.uk">I
agree with Toby's points a,b,c below. I even agree that placement
of the bar cannot prevent the disadvantage.
<br>
<br>
Where we disagree is with the use of the BGA table in setting the
bar.
<br>
<br>
There is plenty of evidence to show that you cannot set the bar
based on the number of rounds alone. For a 6 round tournament,
the BGA tables advise you to have a population range from 7 to 15
players, and in some tournaments that would lead to a range from
5k to 2d or worse.
<br>
<br>
It is essential to take account of the grade distribution at the
top, and the bar depth idea is just a first step in trying to do
this. I have created a spreadsheet showing bar-grade data for all
our tournaments this year.
<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.kaniuk.co.uk/articles/pairing/bga-bar-grades-2018.xls">http://www.kaniuk.co.uk/articles/pairing/bga-bar-grades-2018.xls</a>
<br>
<br>
It has a table on the sheet 'pwin' showing the probability that
player with grade Glo (column A) beats player with grade Ghi (row
3)
<br>
<br>
In the sheet 'tours-pub' we have an anonymised table of
tournaments presented in bar-depth order. It shows who the winner
played and I have detailed the few cases where the winner dropped
a game. This happened in just 5 out of 25 tournaments and in
nearly all such cases the grade difference was just one.
<br>
<br>
There is data showing the probability that the player at the
bottom of the bar (with grade Gbar) beats the maximum graded
player. There were 7 tournaments where the bar-depth varies from 4
to 7. In these tournaments the Gbar player has a winning chance
against the strongest in the range 0.1% to 8.2%
<br>
<br>
For the 10 tournaments with a bar-depth of 1 or 2 this probability
lies in the range 18.1% to 34.1%
<br>
<br>
For the 8 tournaments with bar-depth = 3, the range is 10.7% to
26.1%
<br>
<br>
The spreadsheet also contains a useful plot of these probs vs
bar-depth
<br>
<br>
Remember that these probabilities are calculated for just one
game. The actual probability of a Gbar winning the tournament is
usually tiny.
<br>
<br>
My conclusion is that when the population at a bar-depth of 3 is
small, (varying from 1 to 8) the bar can only be lowered if you
are prepared to consider using handicaps above the bar.
<br>
<br>
If we do not want to do that then one possibility is to isolate
the top group by boosting the initial MMS by a few points - in
other words create a super group. This protects the players below
the bar from hugely unbalanced games.
<br>
<br>
Geoff
<br>
<br>
33 Ashbury Close, Cambridge CB1 3RW 01223 710582
<br>
<br>
On 08/11/2018 09:47, TobyManning via tournament-org wrote:
<br>
<blockquote type="cite">Geoff:
<br>
<br>
Thanks for the extra information.
<br>
<br>
However, I revert to my intiial question:
<br>
<br>
Which is more inportant, to*restrict the bar depth* or to have
the*number of people above the bar compliant with the Table* in
the handbook
(<a class="moz-txt-link-freetext" href="http://www.britgo.org/organisers/handbook/tournament4">http://www.britgo.org/organisers/handbook/tournament4</a>).
<br>
<br>
It is still my view that the Table limits shuld be paramount,
and the bar depth should be used to determine the bar within
these limits.
<br>
<br>
I have re-read your article in BGJ #173, which discusses how
effectively the MacMahon system gives people an even spread of
opponents.
<br>
<br>
We need to recognise that, *irrespective of where the bar* is
set:-
<br>
<br>
a) those at the very top (the 4 dans) will have more "easy"
games and we expect them to have an above-average result
<br>
<br>
b) those well below the bar (the 5 kyus, say) will have a 50:50
result on average
<br>
<br>
c) there is a cohort of people - in the 3 peaks case the 2d/1d -
who will have a below-average result as they will each have to
play the 4 dans at some time.**
<br>
<br>
So placement of the bar cannot prevent this disadvantagement; it
merely alters the make up of the cohort in my group (c) above.
<br>
<br>
In the 3 peaks example, with entry at 4d/4d/2d/1d/1d/1k/1k/1k,
this disadvantagement is effectively the same whether the bar
is set at 4 dan, 3 dan, 2 dan or 1 dan. This is because the
actual games played will be unaffected (each 4 dan is expected
to have opponents 4d 2d 1d 1d 1k irrespective of the bar
setting). With the bar at 1 kyu the disadvantagement is
slightly more widespread and the total disadvantagement starts
to increase, and this then falls off a cliff with the bar at 2
kyu and below.
<br>
<br>
In fact, the disadvantagement is essentially constant while the
number of people above the bar is less than (n+1) where n is the
number of rounds. As the number of people above the bar
increases from (n+1) to 2**n this total disadvantagement
increases - the amount of the increase depending upon the bar
depth. So if the bar depth is shallow the number above the bar
should tend towards n**2, if it is deep it should tend towards
(n+1).
<br>
<br>
There is therefore no benefit from having the number above the
bar being less than (n+1); and indeed it would prevent the
(rogue) 1 dan/1 kyu winning the tournament, irrespective of
their results against the 4 dans.
<br>
<br>
*Manual Overrides*
<br>
<br>
You are quite right to emphasise that TD's can override GoDraw's
defaults. However, my experience is that many TD's -
particularly the inexperienced ones - are reluctant to do this
as they are concerned about possible unintended consequences.
<br>
<br>
I think this emphasises the importance of getting the GoDraw
defaults as good as we can.
<br>
<br>
Toby
<br>
<br>
**I speak from (not really bitter) experience.
<br>
</blockquote>
<br>
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<br>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Toby Manning
26 Groby Lane
Newtown Linford
LE6 0HH
01530 245298</pre>
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