For each Pairs event, the computer system calculates a “Nett” or “Handicap” result as well as the gross result which is produced by the normal scoring program such as Scorebridge or ASE.
What the handicap calculation tries to do is to work out a “nett percentage score” for each pair in a session by allowing for both the ability of the two players in the pair and for the relative standard of the various sessions run throughout the week.
The system consists of three main programs.
1. Assessing the standard of the various bridge sessions held throughout the week
2. Calculating the Handicap Percentage of each Player who regularly plays at the Club
3. Automatic Calculation of Nett Scores for each Session
This aspect is expressed as a percentage “Session rating” for each session during the week. It measures how difficult it is to achieve a percentage score of 50% for each regular session compared with an arbitrary “Standard Session” which is taken as Monday Evening.
This rather complex analysis of past results is run annually and bases its results only on the results of players who play frequently in more than one regular session to see how their average scores compare between the various sessions.
At present, the “Session ratings” are approximately as follows:
Monday Afternoon - 92.0%
Monday Evening - 100%
Wednesday Daytime - 97.4%
Thursday Evening - 104.1%
Friday Daytime - 93.0%
Saturday Daytime - 85.9%
Tuesday sessions are not handicapped for several technical reasons.
The system maintains a database which contains all of the pairs results for the last five years or so.
This program is run approximately every three months and all new results are added to the database.
A long-term moving average is then calculated for every player on the database as follows.
Every result for each player is examined from the first to the most recent.
A percentage “nett score” is calculated for the player for each successive session essentially as described below in the section “Automatic calculation of Nett Scores for each Session”.
The “nett score” so calculated is standardised in terms of a Monday Evening score by multiplying it by the “session rating” for that session.
A new handicap is then calculated with the formula:
[Handicap after this session] = [Handicap before this session] X 0.95 + [Handicap for this session] X 0.05.
This calculates a statistical average, giving 95% of the weighting to past history and only 5% to a single value and so ensures that the handicap does not fluctuate wildly.
A player’s starting handicap is normally 50%, unless previous history from earlier data is available. This arbitrary start value virtually disappears after 20 sessions played.
This program is run as part of the regular computer scoring procedure after each session.
The scoring procedure automatically generates a detailed file of the results for each pair, including names, ABF numbers and percentage scores and starts a separate program to calculate and print out the nett scores for each report as follows.
Each pair who played is examined in turn.
The two handicap percentages are extracted from the database and their combined handicap is calculated as the simple average, which is an estimate of the “ability” of that pair.
For example, a pair with handicaps of 51% and 59% respectively, will get a combined handicap of 55%. They would be expected to score, on average, 55% on Monday evening but only (55 / 1.041) = 52.83% on a Thursday evening.
If they actually scored only 48% on a particular Thursday (4.83% less than “par”), their Nett score would be calculated as (50 – 4.83) = 45.17%.
The pairs playing are then sorted in order of their Nett score and listed on a report which is available on the internet and printed on the club notice-board.
An extract from a typical “Nett score Report” is given below, with only the leading scores shown.
The handicap for each pair is presented as the difference between their Nett score and their Gross score, calculated as above for the particular daily session they played in – in this example Friday morning.
Pairs with better than average ability show as negative numbers and weaker players as positive.
Nett Results - Single Field
Friday 25 July 08
Friday Pairs
Players Hcap Nett Gross
One Field
1 Daryl Moore, Paul Broughton +5.58 56.34% 50.76%
2 Jill Cattell, George Lewis +1.40 55.95% 54.55%
3
4 Daphne Armitage, Sue Currey -1.84 54.07% 55.91%
5 Jennifer Atkinson, Rosalie Broughton -6.13 53.72% 59.85%
6 Sandra Morris, Jan Maddern -0.49 53.60% 54.09%
Roy Low
December 17 2008