[tournament-org] The Bar in general

Fri Nov 23 18:32:51 GMT 2018

Tomorrow at Coventry th entry is 5d 4d 5*1d 1k.

The Bar is therefore logically at 1 kyu.

I will check with the organisers what the software is saying.

Toby

On 09/11/2018 14:51, Geoff Kaniuk via tournament-org wrote:
> Thanks Toby,
>
> There were a couple of typos in the spreadsheet and I have re-issued it.
>
> Geoff
>
> 33 Ashbury Close, Cambridge CB1 3RW 01223 710582
>
> On 08/11/2018 15:55, TobyManning via tournament-org wrote:
>> 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.
> [[
> I think supergroup is a useful tool when:
> a. There are a lot of strong players within a narrow grade range.
> b. There is an excessive grade gap to the next group down.
>
> I am not sure about using just the average grade.  You might want for 
> example to isolate the top group from the rest for the first few 
> rounds but allow mixing for the last two say.
>
> One of the issues with this may be the effect on Stacey points. One 
> solution for this and the small bar or handicap problem, could be to 
> have a Pairing Bar for actually doing the draw and a possibly 
> different Stacey Bar for awarding Stacey points.
>
> But again that is another debate that would need to happen.
> ]]
>
>
>>
>> *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
> [[ Agreed - this was a bar change after the event ]]
>
>>
>> b) Nos 16 and 19: why did the 1k not play both 3k in No 16? 
> [[
> There were quite a number of uneven games after round 2.  The 3k were 
> losing most of their games.
> ]]
>
>
>> Were handicaps used in No 19? 
> [[
> Handicaps are indicated in the opponent list (h)
> In this tournament all players were below the bar.
> ]]
> Both cases are difficult ,
> [[
> Not difficult once one has the full story!
> ]]
>  and there might be a
>> case for handicaps (consult the players?)
> [[
> I know consultation has been mooted. I am not comfortable with this 
> idea, as there can be problems if one player refuses.
> ]]
>>
>> c) No 25 The bar should have been at 1k with a supergroup.
> [[
> This would have made the bar depth 5 with a 1k vs 5d a possibility.
> ]]
>
>>
>> No 1 should have had the bar at 1 dan , when the depth would have 
>> been 3.
> [[
> The maximum grade was 5d.
> With the bar at 1d, the bar depth is 5d - 1d = 4
>
> In this tournament we have 4 rounds with exactly 16 above the bar. I 
> assume this was to get a unique winner.
> ]]
>>
>> In addition, No 13 should be a supergroup (see above) with the bar at 1d
> [[
> The bar *is* 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.
>>
> [[
> For no 7 the TD had the option:
> Bar at 1d pop 5 so 3 below maximum
> Bar at 1k pop 9 so 1 above maximum
>
> I can imagine TD choosing least deviation, but I agree with 1d.
>
> For no 21, sorry my mistake: the number of rounds is 6.
> ]]
>
>> *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: 
> [[
> No chance!
>
> Take the case of no 21 - a 6 round tournament. The table allows a 
> maximum of 15 players above the bar. In this tournament the grade 
> range of players above the bar could be from 6k to 2d. A 6k beats a 2d 
> with probability 0.1%.
>
> Or take number 6, a 5 rounder where the tables allow a population of 12.
> In this case once could have a grade range from 5k to 4d. Winning 
> chance is now less than 0.01%
>
> I realise slightly unfair data as you do not see the full picture but 
> any of the longer tournaments will have this possibility.
> ]]
>
> 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).
>>
> [[
> The bar was at 2k, James was 3k on 4 wins last round, you on 3 wins.
> Both have same mms of 1. James wins. MMS James = 2, MMS Toby=1.
>
> James gets the chocolate!
>
> No outcry, everybody cheers!
> ]]
>
>> 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.
>
> [[
> The lower range of the table is based on the idea that the top players 
> engage in an all-play-all: players = 1 more than number of rounds. 
> However all-play-all is a closed system.  McMahon is open in the sense 
> that after round 1 there are players from below the bar now able to 
> play losers from above the bar. So the top players do not get an 
> all-play-all.
>
> The upper range of the table is a compromise. It starts with the rule
> N=2^R for R = 3 and 4 rounds. This is the rule for a perfect Swiss 
> guaranteeing a unique winner.  Note also that exactly 8 or 16 players 
> are needed and often we do not have exactly that number. So no 
> guarantee of a unique winner.
>
> For R=5, practicality sets in, and I am guessing that our founding 
> fathers realised that to get 32 players above the bar would be 
> difficult so it was set at 12. This would have been based on some 
> experience or just guesswork.
>
> We now have a much better model to determine where the bar should be 
> set. A modified table + the bar-depth filter is a first step in 
> implementing that model.
> ]]
>>
>> Perhaps I should shut up and let others comment.
>
> [[
> I welcome your comments and I hope to hear from others.
> ]]
>
>>
>> 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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>>
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-- 
Toby Manning
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