XG Grades are an adaptation of the National Grade System (NGS) implemented by the English Bridge Union. A National Grade (NG) is an assessment of the playing standard of all affiliated members. Full details of the EBU NGS is available here.

• A players NG is based on their club and tournament results over their last 2000 boards played. For the typical player, this amounts to about 80 sessions.
• The NG is a weighted average calculation where recent results have a higher weighting than older results.
• “Average” players will have an NG of around 50%, and more experienced players will have higher NG, say 55% to 70%.
• After every session, the NG is re-calculated for all participants in that session. The calculation is based on a comparison between the actual scored percentage and each of the players Expected Score.
• The player's Expected Score (ES) is based on
  • The players own current NG.
  • Their partner's current NG.
  • The average current NG for all the pairs they are competing against.
• An NG is calculated for all individual players and for pair combinations.
• The NG is expressed as a percentage that range from about 40% to 70%
• Any player must play a minimum of 150 board before their NG is valid.
• Any session results more than 3 years old are excluded from the calculations.

Included session types are

• Duplicate pairs events scored as match points or IMPs.
• Multiple teams events scored as match points or IMPs.
• Swiss Pairs events scored as match points or IMPs.
• Swiss or Round Robin Teams events. This is based on the pairs cross-IMP Butler result.

 

		Assume …	
                            your current NGS   =   55%
                   your partner’s current NG   =   61%
                    the opponents average XG   =   52%

         In this session, the Expected Score   is   50%
                                        plus       Average of you and your partners current NG
                                        less       Average of the opponents NG
										
                                               =   50  +  (55 + 61)  / 2  - 52 
                                               =   56% 

        If the pair scored 57% for the session, the partnership has scored 1% (57 less 56)
        ABOVE expectation, so this has a positive effect on your NG.
				

		Assume this pair is playing in a much stronger field where the opposition's 
		average XG is 60%	
                            your current NGS   =   55%
                   your partner’s current NG   =   61%
                    the opponents average XG   =   60%

         In this session, the Expected Score   is   50%
                                        plus       Average of you and your partners current NG
                                        less       Average of the opponents NG
										
                                               =   50  +  (55 + 61)  / 2  - 60 
                                               =   46% 

        If the pair scored 57% for the session, the partnership has scored 11% (57 less 46) 
        ABOVE expectation, so this has a very positive effect on your NG.
				

		Assume this pair is playing in a much weaker field where the opposition 
		average XG is 47%	
                            your current NGS   =   55%
                   your partner’s current NG   =   61%
                    the opponents average XG   =   47%

         In this session, the Expected Score   is  50%
                                        plus       Average of you and your partners current NG
                                        less       Average of the opponents NG
										
                                               =   50  +  (55 + 61)  / 2  - 47 
                                               =   61% 

        If the pair scored 57% for the session, the partnership has scored 4% (57 less 61) 
        BELOW expectation, so this has a negative on your NG.
				

Bottom line

• If you play above expectations, your NG will increase. Conversely, if you play below expectations, your NG will decrease.
• If you play with a good player and play poorly, your NG will decrease
• If you play with a good player and play quite well, your NG will probably not change
• If you play with a good player and play very well, your NG will increase a little
• If you play with an inexperienced player and play quite well, your NG will increase
• If you play with an inexperienced player and play very well, your NG will increase

As the NG recalculations are dependent on many factors, it is difficult to predict how the NG changes from session to session. A rough rule of thumb is that, for every 1% variation from the expected score, the XG will change by about 0.025% (give or take).

XG Grades are calculated for all participants is the weekly XClub competitions. Some facts and figures:

• Approximately 45 NZ clubs, and 4000 players participate in the XClub competition.
• All participating clubs play the same hands in each session.
• The participating clubs can use any of the scoring system currently used is New Zealand ie Compass or Scorer or CompScore2.
• The across-the-board result is calculated for each session and it is this score that is used in the XG calculations.
• XG Grades are calculated for individual players only (ie XG Grades are not calculated for pairs)
• The new XG Grades are calculated at the end of each week and published on the XClub website and on this website.

XG (and NG) grades are perfect for club handicapping. There are two options for the applied handicaps:

1. Simply use the players NG
2. Use the pairs Expected Score (ES)

Option 2 is preferable as it considers the playing strength of the competing field. For example

• If an average pair is playing in an average field, their ES will be about 50%
• If an average pair is playing in a more experienced field, their ES will be less than 50%
• If an average pair is playing in a less experienced field, their ES will be higher than 50%
• It is possible that the strength of the NS pairs is significantly different from the strength of the EW pairs. ES handicapping takes this into account.

The calculations for Expected Score handicapping is more complicated as the current NG Grades is used required for all participants in any session. The Compass Scoring System does these calculations automatically.

This example is from the Matamata Bridge Club. Note that Compass users can this view type of report from the View Results in Notepad ... Results - Handicap (XG) menu option on the View Session Results screen.

	
				
		Handicap Champs  Session  1 Handicap: XG Handicap   08 July 2021

 N-S 
         Total Players         8
         XG Average          56.11            Opps       Player       Pair Expected  Exp      Raw    H/Cap
                                               XG          XGs         XG    Score  Score H/C Score  Score
 ----------------------------------------------------------------------------------------------------------
 1   Lesley Quilty & Joy Williams             55.62   61.64 + 57.39   59.52   53.89   -3.89   65.77   61.88
 2   Michele Liddle & Ian Bond                56.12   52.32 + 59.74   56.03   49.91    0.09   55.36   55.45
 3   Ken Yule & Kathy Yule                    55.10   62.19 + 64.16   63.18   58.08   -8.08   61.31   53.23
 4   Lynette Morgan & Guy Kalma               56.08   59.78 + 52.86   56.32   50.24   -0.24   53.27   53.03
 5   Rachel Aylett & Joanne Swanwick          56.91   40.12 + 60.94   50.53   43.62    6.38   45.54   51.92
 6   Malcolm Kirkby & Laurie Belfield         56.03   56.50 + 56.88   56.69   50.66   -0.66   45.54   44.88
 7   Henk Hemmes & Judith Howard              56.33   50.23 + 58.91   54.57   48.24    1.76   42.86   44.62
 8   Elaine Saywell & Helen Reid              56.69   52.72 + 51.37   52.05   45.36    4.65   30.36   35.01


 E-W 
         Total Players         8
         XG Average          49.38            Opps       Player       Pair Expected  Exp      Raw    H/Cap
                                               XG          XGs         XG    Score  Score H/C Score  Score
 ----------------------------------------------------------------------------------------------------------
 1   Joan Darby-Smith & Beth Vosper           49.39   48.55 + 49.96   49.26   49.86    0.14   60.42   60.56
 2   Hermanna Hemmes & Fritz Vibelund         48.41   57.50 + 54.77   56.14   57.72   -7.72   64.58   56.86
 3   Saskia van Waaijenburg & Julie Morgan    50.86   39.00 + 39.00   39.00   38.14   11.86   44.94   56.80
 4   Colin Le Quesne & Anne Beetham           48.70   50.71 + 57.56   54.14   55.44   -5.44   58.33   52.89
 5   Maeleen Borkin & Lorraine Vickers        49.89   46.22 + 45.41   45.82   45.93    4.07   42.56   46.63
 6   Austin Brown & Ross McIntyre             50.13   40.75 + 47.48   44.12   43.99    6.01   38.69   44.70
 7   Dale Swap & Sonia Crawford               48.57   53.06 + 56.94   55.00   56.43   -6.43   48.21   41.78
 8   Moya Young & Coral Daisley               49.07   51.33 + 51.79   51.56   52.50   -2.50   42.26   39.76
		
				

• The date of the session is 8 July 2021. The XG information for each player is the most recent XG information prior to 8 July 2021.
• The average XG of the NS pairs is 56.11%, and the EW average is 49.38%. This indicates that the NS pairs are quite a stronger than the EW pairs.
• The Opps XG (Opposition XG), is the average XG of all other players seated in the same direction (excluding themselves).
• Ken and Kathy are the strongest NS pair with an average XG of 63.18. The average of their opposition is 55.10
• Rachel and Joanne have the lowest XG of the NS pairs. The average of their opposition is 56.91
• The Expected Score for each pair is 50 plus Pair XG less Opps XG
• Thus Ken and Kathy have an Expected Score of 58.08 and Rachel and Joanne have an Expected Score of 43.62.
• These Expected Scores then translate to the handicaps (Exp Score H/C) for this specific session. Ken and Kathy have a handicap of -8.08% and Rachel and Joanne have a handicap of +6.38%.
• The actual Raw Scores and the H/cap Scores are displayed in the last 2 columns.

Some What-ifs ...

• If Ken and Kathy were seated EW, they would have been in a much weaker direction. Their Expected Score would have been about 50 + 63 - 50 = 63%, ie about 5% greater than their NS Expected Score
• If Rachel and Joanne were seated EW, they would have been in a much weaker direction. Their Expected Score would have been about 50 + 50 - 50 = 50%, ie about 6% less than their NS Expected Score
• The above two examples show the beauty, and fairness, of Expected Score handicapping

Bob Fearn
July 2021