[tournament-org] The Bar in general

Thu Nov 8 15:55:01 GMT 2018

Geoff:

Thanks.

*Supergroup*

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 *average* 
strength not simply "bar+1".

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.

*Spreadsheet Comments*

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:-

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

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?)

c) No 25 The bar should have been at 1k with a supergroup.

No 1 should have had the bar at 1 dan , when the depth would have been 3.

In addition, No 13 should be a supergroup (see above) with the bar at 1d

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.

*Use of Organiser's Handbook Tables*

You state:-

/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/.

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 http://www.britgo.org/results/2017/threepeaks).

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.

Perhaps I should shut up and let others comment.

Toby.

On 08/11/2018 14:28, Geoff Kaniuk via tournament-org wrote:
> I agree with Toby's points a,b,c below.  I even agree that placement 
> of the bar cannot prevent the disadvantage.
>
> Where we disagree is with the use of the BGA table in setting the bar.
>
> 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.
>
> 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.
>
> http://www.kaniuk.co.uk/articles/pairing/bga-bar-grades-2018.xls
>
> 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)
>
> 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.
>
> 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%
>
> For the 10 tournaments with a bar-depth of 1 or 2 this probability 
> lies in the range 18.1% to 34.1%
>
> For the 8 tournaments with bar-depth = 3, the range is 10.7% to 26.1%
>
> The spreadsheet also contains a useful plot of these probs vs bar-depth
>
> Remember that these probabilities are calculated for just one game.  
> The actual probability of a Gbar winning the tournament is usually tiny.
>
> 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.
>
> 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.
>
> Geoff
>
> 33 Ashbury Close, Cambridge CB1 3RW 01223 710582
>
> On 08/11/2018 09:47, TobyManning via tournament-org wrote:
>> Geoff:
>>
>> Thanks for the extra information.
>>
>> However, I revert to my intiial question:
>>
>> 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 (http://www.britgo.org/organisers/handbook/tournament4).
>>
>> 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.
>>
>> I have re-read your article in BGJ #173, which discusses how 
>> effectively the MacMahon system gives people an even spread of 
>> opponents.
>>
>> We need to recognise that, *irrespective of where the bar* is set:-
>>
>> a) those at the very top (the 4 dans) will have more "easy" games and 
>> we expect them to have an above-average result
>>
>> b) those well below the bar (the 5 kyus, say) will have a 50:50 
>> result on average
>>
>> 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.**
>>
>> So placement of the bar cannot prevent this disadvantagement; it 
>> merely alters the make up of the cohort in my group (c) above.
>>
>> 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.
>>
>> 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).
>>
>> 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.
>>
>> *Manual Overrides*
>>
>> 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.
>>
>> I think this emphasises the importance of getting the GoDraw defaults 
>> as good as we can.
>>
>> Toby
>>
>> **I speak from (not really bitter) experience.
>
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-- 
Toby Manning
26 Groby Lane
Newtown Linford
LE6 0HH
01530 245298

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