Calculating Bridge Tournaments

General Principles - Bastille

Several problems arise in the Butler system, some having to do with problems of rounding. One solution to these problems is to do away with rounding altogether. When using a computer, no rounding is needed. A continuous version of the official WBF IMP-scale has been developed, and has been in use in a special version of the Butler system, called Bastille because it was first used at a tournament of the Royal Squeeze Bridge Club of Antwerp on 14 July 1989 (the 200th anniversary of the storming of the Bastille).

The continuous version of the IMP-scale coïncides with the normal scale at the half-way points. In the discrete table, 0-10 score 0 IMP, 20-40 get 1 IMP, 50-80 equals 2 IMP. In the continuous version, 15 points gives 0.5 IMP, 45 equals 1.5 IMP. The scale is linear through these points.

This means that if one applies the Bastille scoring, and then rounds the IMPs to the nearest integer, this automatically equals the Butler score.

The formulas are :

from	   0	 to   45	 : IMP =  score     	/	 30
from	  45	 to  165	 : IMP = (score +   15)	/	 40
from	 165	 to  365	 : IMP = (score +   60)	/	 50
from	 365	 to  425	 : IMP = (score +  145)	/	 60
from	 425	 to  495	 : IMP = (score +  240)	/	 70
from	 495	 to  595	 : IMP = (score +  555)	/	100
from	 595	 to  895	 : IMP = (score + 1130)	/	150
from	 895	 to 1495	 : IMP = (score + 1805)	/	200
from	1495	 to 2495	 : IMP = (score + 2630)	/	250
over	2495			 : IMP = (score + 7755)	/	500

The use of the Bastille system would have prevented the strange results that occurred in Scheveningen in early 1994. At that tournament, the correction of a result in favour of Hamman-Wolff cost them a place and several hundreds of guilders.

In the last round of that tournament, a board had been scored 2NT+1 : +180. The opponents on the board, Mrss Hamman-Wolff, sought and got a rectification. They expected to gain one IMP and consequently one place, but instead lost one place and 2000 dutch guilders.

What had happened ?

Together with a change of score, this rectification induced a change of datum-score, the average with which all scores are compared. This average fell from +240 to +230.

Hamman-Wolff originally got 240-180 = 60 = 2 IMP After the rectification, this became 230-150 = 80 = 2 IMP

On the other hand, the dutch pair of Leufkens-Westra (playing North-South) originally scored 400-240 = 160 = 4 IMP. This became 400-230 = 170 = 5 IMP, gaining them one IMP and a lone sixth place (originally they had been classed equal sixths).

What would the Bastille scoring have made of this ?

We can only guess at the original average, before rounding. Let us suppose this was +237. (any other average between 235 and 240 will give the same outcome) The original score for Hamman-Wolff was : 237-180 = 57 = 1.8 IMP The original score for Leufkens-Westra was : 400-237 = 163 = 4.45 IMP

After recalculation, the average would go down 5 points (the average is calculated without using the two outermost scores; there were 8 tables, so the average is a total divided by 6) and would, in our presumtion, now be +232. As you can see, this coïncides beautifully with the Butler change from 240 to 230.

Now Hamman-Wollf would score : 232-150 = 82 = 2.425 IMP (gain +.625) And Leufkens-Westra : 400-232 = 168 = 4.56 IMP (gain +.11)

As we can see, the rounded IMPs for Hamman-Wolff remain at +2, those for Leufkens-Westra jump over the 4.5 mark and give an extra IMP. This is exactly the result of the Butler version.

The very nature of the Duplicate Bridge Game makes that every good thing you do, also helps your 'friends', meaning those that play at other tables in the opposite direction. Yet a system that permits these 'helpings' to be greater than your own benefit can surely do with some improvements.

Last Modified : 1996-07-03