Page 0018

National Grading Scheme by Mike Christie

Now that the National Grading Scheme (NGS) has been live for over six months, we asked Mike Christie,

who heads the team implementing the scheme, to answer some more of the most common questions.

What is ‘Par’? have a numeric grade of over 67%. which has few visiting players. Both types

of group are likely to be weaker than the

THE BASIC question I get asked is what EBU average, but the NGS has few results

does my grade mean? It is the ‘par’ score to shift the group’s average grade away

you and your partner would achieve when from its starting value, so these players

playing a session of match-pointed pairs tend to be over-graded. However, pro-

with a player of the same grade against vided there is some mixing, either into the

average opponents. If your partner has a group or outwards from the group, the

different grade from you, take the average group’s average grade will gradually shift

of your grades. If you play in a session that towards its correct value. We’ve called this

is stronger than the EBU average, say by process ‘Diffusion’ and its speed depends

three points, then your par for that session on the degree of mixing. It has already

is lower by 3 points. Conversely against been effective for many clubs and sessions.

weaker opponents you’re expected to do There are around a hundred sessions a

better so your par score for that session is week with an average strength below 46

higher. and several regular ‘gentle’ sessions now

The 'par' score is what you and your have an average strength in the mid- to

partner need to beat to improve your low-forties, which demonstrates that dif-

current grades (this is a slight simpli- fusion is working. However, in some cases

fication). So, for example. if someone with diffusion is likely to take years rather than

grade around 53 plays with a partner with Accuracy of Your Grade months to complete.

grade 49, they need to score over 51% to

beat par against an average field, but only You probably know someone who is much Regular Partnerships

need to score above 48% to beat par stronger or weaker than their grade seems

against the stronger field mentioned to imply. So how accurate are NGS grades? The other exceptions are pairs who almost

above. How significant is the difference between always play together, but who occasionally

When my regular partner and I go to an ‘Eight’ and a ‘Ten’, say? play with other partners. As with all

play a session of bridge, we calculate this For the large majority of players, their partnerships, NGS uses the results to

par value, and have that as a mental target grade will be within one band (2%) of calculate both a partnership grade and

for the evening, so we can go home happy their true current strength over half of the individual grades for the pair. NGS uses

if we beat par even though we don't get time and within two bands (4%) over the sessions they’ve played with other

into the top three places, knowing that we ninety per cent of the time. So don’t fuss if partners to estimate their individual

have each improved our NGS grade. your greatest rival is ahead of you by one grades. This is OK except when there

grade band. By the way, this only applies aren’t enough of these occasional sessions.

Grade Bands once you’ve played at least 1000 graded As an example, take Ann and Bob who

boards, at which point your grade is said have partnered each other every week over

We use numeric grades for calculations to be mature. Before this, your grade is the last two years apart from five times

like the above, but for descriptive ‘Evolving’, and is denoted by putting an ‘e’ when they each played with other

purposes EBU grades have been divided after the grade. partners. Ann did much better than par in

into thirteen playing card bands, ranging There are two exceptions, where NGS these sessions, but Bob didn’t. The same

from ‘Ace’ at the top to ‘Two’ at the can’t be relied on to be this accurate. factors that make diffusion work also

beginners’ end. Grade band ‘Eight’ is in the The first of these are groups of players make NGS quick to use Ann’s better-than-

middle and since each grade band is 2% who are isolated from the rest of the EBU par results with other players to give her a

wide, an ‘Eight’ covers the range 49-51%. in terms of the sessions they play. One higher grade than Bob, and Ann’s grade is

The ‘Ace’ band covers all grades 61% example is the group of players in the eight points above Bob’s.

upwards, and the Aces have been divided ‘gentle’ or ‘improvers’ sessions of a club, if We recently examined around a dozen

into four further bands, Ace of Clubs, none of them play in other sessions. similar examples where the players in the

Diamonds, Hearts, and Spades. So the fifty Another example is a club nearly all of pair had a grade difference of over eight

or so players in the Ace of Spades band all whose members only play at that club and points. In most of these cases it looks as

18 English Bridge October 2012 www.ebu.co.uk

Index

  1. Issue 243
  2. Page 0002
  3. Page 0003
  4. Page 0004
  5. Page 0005
  6. Page 0006
  7. Page 0007
  8. Page 0008
  9. Page 0009
  10. Page 0010
  11. Page 0011
  12. Page 0012
  13. Page 0013
  14. Page 0014
  15. Page 0015
  16. Page 0016
  17. Page 0017
  18. Page 0018
  19. Page 0019
  20. Page 0020
  21. Page 0021
  22. Page 0022
  23. Page 0023
  24. Page 0024
  25. Page 0025
  26. Page 0026
  27. Page 0027
  28. Page 0028
  29. Page 0029
  30. Page 0030
  31. Page 0031
  32. Page 0032
  33. Page 0033
  34. Page 0034
  35. Page 0035
  36. Page 0036
  37. Page 0037
  38. Page 0038
  39. Page 0039
  40. Page 0040
  41. Page 0041
  42. Page 0042
  43. Page 0043
  44. Page 0044
  45. Page 0045
  46. Page 0046
  47. Page 0047
  48. Page 0048
  49. Page 0049
  50. Page 0050
  51. Page 0051
  52. Page 0052
  53. Page 0053
  54. Page 0054
  55. Page 0055
  56. Page 0056