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<p>Re the point on TD overrides...<br /><br />At our small local tournaments which do not have heavy prize money the TD aim should be a great tournament for everyone. Hence the TD should have discretion to do what he / she thinks fit to make this happen. If this means fixing the draw so that siblings do not play or that the two 5 dans do not meet in round 1 then they should use their discretion to do so. <br /><br />Until we move to the chess tournament model of lots of prize money right down a tournament (in which case people become very concerned about draws and fairness of tiebreaks) we have the ability to use a lot or common senses when running events. </p>
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<div class="pre" style="margin: 0; padding: 0; font-family: monospace">Alison Bexfield</div>
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<p>On 08/11/2018 09:47, TobyManning via tournament-org wrote:</p>
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<p>Geoff:</p>
<p>Thanks for the extra information.</p>
<p>However, I revert to my intiial question:</p>
<p>Which is more inportant, to<strong> restrict the bar depth</strong> or to have the<strong> number of people above the bar compliant with the Table</strong> in the handbook (<a class="moz-txt-link-freetext" href="http://www.britgo.org/organisers/handbook/tournament4" target="_blank" rel="noopener noreferrer">http://www.britgo.org/organisers/handbook/tournament4</a>).</p>
<p>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.</p>
<p>I have re-read your article in BGJ #173, which discusses how effectively the MacMahon system gives people an even spread of opponents.</p>
<p>We need to recognise that, <strong>irrespective of where the bar</strong> is set:-</p>
<p>a) those at the very top (the 4 dans) will have more "easy" games and we expect them to have an above-average result</p>
<p>b) those well below the bar (the 5 kyus, say) will have a 50:50 result on average</p>
<p>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.** </p>
<p>So placement of the bar cannot prevent this disadvantagement; it merely alters the make up of the cohort in my group (c) above.</p>
<p>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.</p>
<p>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).</p>
<p>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.</p>
<p><strong>Manual Overrides</strong></p>
<p>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. </p>
<p>I think this emphasises the importance of getting the GoDraw defaults as good as we can.</p>
<p>Toby</p>
<p>**I speak from (not really bitter) experience.</p>
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<div class="moz-cite-prefix">On 07/11/2018 13:31, Geoff Kaniuk via tournament-org wrote:</div>
<blockquote type="cite" style="padding: 0 0.4em; border-left: #1010ff 2px solid; margin: 0">A. THREE PEAKS <br /> The 3P incident was interesting. I has a conversation with Bob after the event and it transpired that initially Bob had a top group of 6 players something like 5d,4d, 1k,1k, 1k,1k. After closing the register GoDraw set the bar at 1k, as this provides a jump from 2 to 6 players, even though the bar-depth exceeds 3. <br /><br /> At this point two more players pitched up: a 2d and a 1d. I am not sure if Bob had already done the draw, but there would have been no problem - just pair them and sort out the draw later after entering results. This would have left the bar at 1k as it does not get re-computed. <br /><br /> I assume he had not done the draw, and may have tried to add these two players. This would be refused by GoDraw because it had already worked out the bar. Now you have to re-open the register, add the two players, and close the register. <br /><br /> Now GoDraw sets the bar afresh. At 2d the bar depth is 3 but still not enough players to exceed the number of rounds. So it leaves the bar at 4d. <br /><br /> I do understand the tension involved in getting the first round going, so Bob did the right thing and carried on with the draw. But actually there is a simple way to deal with this: <br /><br /> After closing the register, <br /> If you do not like the bar, <br /> Just change it! <br /><br /> There is a field for setting the bar manually and you can adjust it to what you want. The philosophy underlying GoDraw is that it is a TD's toolkit, not a TD's boss! <br /><br /> You cannot change the bar after doing the draw. The only thing setting the bar does, is to specify the player's initial McMahon score. Again there is a field in the register editor which allows you to change the player's initial MMS and this of course adjusts the players current MMS as well. By making this adjustment for all the players you want above the bar, you achieve what you want! <br /><br /> B. THE BGA BAR TABLE CONDITIONS <br /> Toby reproduces four conditions which an ideal bar setting should meet. These are indeed aspirations. But on their own they do not provide any information that is useful for setting the bar. A 5 round tournament would require exactly 32 players above the bar to guarantee a unique winner. Three Peaks had a total of 34 so almost everybody above the bar?. It might be well worth while having a look at BGJ 173 - Finding the Bar which discusses <br /><br /> C. THE BGA BAR TABLE VALUES <br /> I have in the past tried to find some documentation on the origins of the table and the best I got was that it is lost in the mists of time. <br /><br /> When the table was invented, people did not have a good measure of the probability of win between players of different strengths. But now through the data collected by EGD we do have a good model. This enables us to simulate McMahon tournaments to assess the effect of different bar settings and that work is cited in the BGJ 173 article. <br /><br /> The outcome confirms that you cannot set the bar on the basis of number of rounds alone, but it depends on the nature of the distribution of top grades. It leads to the following table which is a rough linear representation of the extremes of the bar populations in the simulations: <br /><br /> rounds 2 3 4 5 6 7 8 9 10 <br /> low 2 3 4 5 6 7 8 9 10 <br /> high 11 12 14 15 16 18 19 21 22 <br /><br /> In these simulations the bar was calculated by a Monte Carlo algorithm. The bar depth never exceeded 3 and was very rarely equal to 3. <br /><br /> Toby said: <br /> >Of course, the statement on bar depth being less than 3 assumes that >the grades are "correct" in some ill-defined way. <br /><br /> The McMahon system relies on players entering with realistic grades, and so in all my discussions I always assume that grades are consistent with player strengths as found on our rating page. <br /><br /><br /> Geoff <br /><br /> 33 Ashbury Close, Cambridge CB1 3RW 01223 710582 <br /><br /> On 06/11/2018 13:27, TobyManning via tournament-org wrote: <br />
<blockquote type="cite" style="padding: 0 0.4em; border-left: #1010ff 2px solid; margin: 0">Further issues with the Bar at the 3 Peaks... <br /><br /> *Background* <br /><br /> The 3 peaks is a 5 round tournament. The entry was 5d 5d 2d 1d 1d 1k 1k 1k 2k.... and Bob Bagot wanted to put the bar at 1 kyu. However, the software (Go Draw) put it at 5 dan, so in the first round the 2 5 dans played each other (and the 2d played a 1 d). With advice from Geoff - for which many thanks - the bar was restrospectively changed to 1 kyu for rounds 2-5. <br /><br /> Incidentally one of the 5 dans lost to a 1 dan - it can happen. <br /><br /> *Analysis* <br /><br /> The BGA Tournament Handbook (<a class="moz-txt-link-freetext" href="http://www.britgo.org/organisers/handbook/tournament4" target="_blank" rel="noopener noreferrer">http://www.britgo.org/organisers/handbook/tournament4</a>) states (my added emphasis): <br /><br /><br /> /4.2////The Bar/ <br /><br /> /Because a player's starting score is determined by their grade, a player who was 7 dan would have a massive advantage and the best chance to win the tournament, as such a player would start with a very high MMS. To counteract this, and to give as many people as possible a reasonable chance of winning the tournament, players at or above a certain rank all begin at the same MMS. This rank is called the McMahon bar. For example, if the bar is set at 3 dan (which is an MMS of 2) then no player can start at an MMS of more than 2, no matter what his or her grade: 3-dans, and all players stronger than 3-dan, also start with an MMS of 2, and are said to start "above the bar". The position for the bar depends on the number of rounds to be played and also the entry at each of the higher grades. BGA recommended guidelines are as follows:/ <br /><br /> /3 rounds/ /4-8 players/ <br /> /4 rounds/ /5-10 players/ <br /> /5 rounds/ /6-12 players/ <br /> /6 rounds/ /7-15 players/ <br /> /7 rounds/ /8-18 players/ <br /> /8 rounds/ /9-22 players/ <br /> /9 rounds/ /10-26 players/ <br /> /10 rounds/ /11-30 players/ <br /><br /> /These figures attempt to meet the following conditions:/ <br /><br /> * /There must be a unique winner. This sets an absolute upper limit, <br /> of 2//^r ////players above the bar, where r is the number of rounds./ <br /> * /If there are too many above the bar, the tournament will end <br /> without all of the top players having played each other./ <br /> * /If there are too few above the bar, these receive an unfair (and <br /> unnecessary) disadvantage./ <br /> * /Higher graded players should not run out of even game opponents./ <br /><br /> /The McMahon System imposes two quite severe constraints on the pairing of players at each round. The first is the rule that there are no repeat games. This increasingly restricts the opponents of the stronger players in the later rounds. The second is the aim of pairing players on the same MMS, which provides the main pairing diversity in the early rounds.//// <br /> // <br /> //These two pairing rules, together with the nature of the winning probability between players of different grades, provides quite an important ingredient in determining the position of the bar. //*It turns out that players in the bar group have at least some chance of winning the tournament if the difference between the maximum grade and the bar grade (the bar-depth) is less than 3*//, whatever the number of rounds [See BGJ 173 Finding The Bar]./ <br /><br /> /If you are using Geoff Kaniuk's GoDraw to create the draw,//*it will automatically set the bar according to the above table taking into acount the restriction on the bar depth*//. This is particularly effective in tournaments where the dan entry is very fragmented with possible gaps in the higher grades./ <br /><br /><br /> Of course, the statement on bar depth being less than 3 assumes that the grades are "correct" in some ill-defined way. <br /><br /> It is clear that what is happening is the restriction on bar depth is over-riding the recommended nuimbers in the Table. I believe that this is wrong, and that the Table should have supremacy. <br /><br /> The Table is constructed on 2 simple principles:- <br /><br /> a) The total should be less than 2**n (where n is the number of rounds - this ensures a unique winner <br /><br /> b) The Tournament winner's opponents should all have started above the Bar (although one appreciates that this may not have been the case if the number above the bar is odd and the eventual winner is drawn down in their first game). <br /><br /> In the 3 Peaks example,each 5 dan will play 5 opponents, of strength (probably) 5d 2d 1d 1d 1k, and if (for example) one of the 1 dans wins all 5 games, including beating both 5 dans, they shdol win the Tournament. <br /><br /> Of course one can always play handicap games at the top end.... but that is a different debate. <br /><br /> Toby <br /><br /><br /> _______________________________________________ <br /> tournament-org mailing list <br /><a class="moz-txt-link-abbreviated" href="mailto:tournament-org@lists.britgo.org">tournament-org@lists.britgo.org</a> <br /><a class="moz-txt-link-freetext" href="http://lists.britgo.org/cgi-bin/mailman/listinfo/tournament-org" target="_blank" rel="noopener noreferrer">http://lists.britgo.org/cgi-bin/mailman/listinfo/tournament-org</a> <br /><br /></blockquote>
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Toby Manning
26 Groby Lane
Newtown Linford
LE6 0HH
01530 245298</pre>
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