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Simple Overview of Ratings ( PPI)

The Bridge Club Live PPI Scheme

Introduction

Our Past Performance Indicator (PPI) scheme, started in 2002, is a grading scheme and is considered to be one of the best available grading schemes anywhere. The English Bridge Union National Grading Scheme (NGS) is based upon our PPI scheme.
The PPI scheme calculates a figure based upon your recent results, which are expressed as a percentage, thus giving a way for members to monitor how they are doing on a daily or monthly basis. You may look up your own percentage on your profile and even see your PPI history in graphical form.
The primary purpose for having a scheme is to help players find compatible partners. Games involving partners of vastly different standards tend to be very uneven – an inexperienced player partnering a Grand Master may feel extra pressure, while a Grand Master may find it tedious to see partner make elementary plays.
But also, the PPI scheme provides an approximate indication of the standard of the bridge players you are partnering and opposing.

Definition

The PPI figures represent the percentage scores that a player would expect to average if partnering another player with the same PPI against a field of BCL members of average standard. As PPI's are purely based on past performance, they should be considered only as a rough measure of standard and not taken too seriously.
Other members looking at your profile (and vice versa) may see one of eight symbols:

These "solid" card symbols will show your PPI category and indicate you are "active". (ie: having played AT LEAST 50 rated boards in the last 3 calendar months).

These "shaded" card symbols show your current PPI in the same way but you are 'inactive". (ie: having played LESS THAN 50 rated boards in the last 3 calendar months)

How it works

The formula calculates a PPI figure for each player that, expressed as a percentage, could be described as a handicap (as in golf). We occasionally use this as a handicap or as the basis for 'seeding' in some of our Special Competitions.
Your PPI figure is updated after every event in which you play in any rooms except the Social and Coaching Bridge Rooms, and any room with IMP scoring. The update takes place as the event is archived. (The scheme could include IMP scored competitions by using a conversion, but there are no plans for such at the present time.)
The calculations take your partner’s and your opponents' PPIs into account as well as how many boards you play in each event. Remember, there is no advantage for higher standard players to play against less experienced players, as in doing so, their results must be much better than the norm in order to get a positive change in their PPI and the formula is designed to take account of differences in standard between all the players at a table.

The range of PPI figures

There are no artificial limits to the PPI figures. The strongest players have PPI figures of 60% or more and intermediate players could have figures of less than 40%, a difference of 20%.
The spread of PPI figures for players tends to form a Normal Distribution with the obvious mean of around 50% and with a Standard Deviation of around 5%.
What this means is that about 68%, over two thirds, of all members will have a PPI between 45% and 55% and about one sixth will have a PPI above 55% and about one sixth will have a PPI below 45%. Two and a quarter percent of all members will have a PPI above a figure of around 60%.
Bridge Club Live displays PPIs of members by way of one of four suit symbols on the profile of each member. This method has consistently been deemed the most popular in survey polls of members..

PPI  

Suit symbol

Over 55%

 Spade

51% to 55%

Heart

46% to 51%

Diamond

Below 46% 

Club

Having selected these bands, it will therefore be found that :

about 16% of members are denoted with Spade symbols

about 25% of members are denoted with Hearts

about 33% of members are denoted with Diamonds

about 26% of members are denoted with Clubs.

 

Full Details of the scheme

When you play a board in a rated room, your PPI may or may not change depending on your actual score and your expected score based on the PPI of the four players at the table.
For an up-to date listing of which rooms affect PPI, take a look at “Bridge Rooms Timetable”.
Newcomers are assigned an initial PPI of 50%, and your PPI will be seen only after you have played at least 50 qualifying boards
For the calculations, we need to know how many previous rated boards you have played since the start of the scheme, which was the beginning of July 2002. We also need to know how many qualifying boards you have played in the preceding 90 days.

The Formula

At the end of each event, each player’s PPI is updated. The updating is carried out on a board by board basis and in accordance with the following formula:

A = a + ( p –( (a+b-c-d)/2 + 50 ) ) /m

where

m = 30 if k less than 30,
m = k if k is between 30 and 300
m = 300 if k is greater than 300 and if w is less than 150
m = 2w if k is greater than 300 and if w is between 150 and 300
m = 600 if k is greater than 300 and if w is greater than 300

BUT if a is less than 46, the value of m is then halved
and where (using Fred as the player for whom we are calculating)

A = Fred’s new PPI
a = Fred’s existing (ie old) PPI
p = The percentage value of Fred’s score on the board (This will be between 0 and 100)
b = Fred’s partner’s existing PPI
c = Fred’s Left Hand Opponent’s existing PPI
d = Fred’s Right Hand Opponent’s existing PPI
k = The number of qualifying boards that had previously been played by Fred since the start of the scheme within rated MP rooms only (except for boards played when a Guest Member is at the table).
w = The number of qualifying boards that had previously been played by Fred during the previous 3 calendar months within rated MP rooms only (except for boards played when a Guest Member is at the table). - Updated monthly.

The letter “m” is referred to as the weighting factor. It denotes how much weighting to give your updated PPI for the most recent board that you have played. For many players, the weighting factor is 600 so that the most recent board that you play accounts for one six hundredth (or 0.0167%) of your PPI.
However, there are reasons why “m” is not 600 for all players, and this is where all the "k" and “w” stuff come in.
Firstly, new players are artificially assigned an initial PPI of 50% and this can be a long way out, so it's important for the early results to be weighing heavily compared with the limited (or non-existent if he is playing for the first time) "history" of the player. As the player plays more and more boards the weighting factor will gradually increase.

The PPI figure of a newcomer will therefore fluctuate considerably over his first visit or two.

Let's say a newcomer plays at a table where the other three players also have a PPI figure of 50% and over 12 boards the newcomer scores 40% overall. His PPI will go down from 50% to about 46% straight away.

A very inexperienced bridge player could easily see their PPI. Go down from 50% to 35% and then as they gradually become more experienced and a better player, they will see their figure gradually rise up.

In order for the PPI to be more responsive for players who don’t play frequently in the qualifying rooms, whether that be because they play mainly in the IMP or Social rooms, or whether they simply play online infrequently, the weighting of the most recently played qualifying boards will increase for these players.
Thus, there is increased volatility of PPI. for those that play less than 300 qualifying boards in 3 months, equivalent to 3 hours a week, or 2 Daily Tourneys a week. Volatility is doubled for those playing fewer than 150 qualifying boards in 3 months, equivalent to about one Daily Tourney or one 14 board session a week.

From our periodic surveys we noted a strong perception by Club rated players that they find it difficult to rise above this level (The threshold is 46%). We have therefore doubled the volatility for each of the most recent boards (halving the value of “m”) for each player who is below 46%. This will have the effect of enabling a session of good hands to improve your PPI dramatically, and in some cases, move you into the Diamond range, where immediately the calculation will revert to the normal weighting. Conversely, a few bad boards will drop your PPI just as dramatically. We will continue to review this.

Following your PPI

We provide a detailed graph of your own PPI over time which can be accessed from the home page via Members > My Profile and clicking on the actual % showing alongside your PPI symbol. From this page, you can access a further page that gives details of your recent PPI calculations. These are approximate as they take a session as a whole, and the actual PPI calculations are carried out on a board-by-board basis.
It is difficult for members when playing to estimate accurately the scores they need to maintain their PPI as the use of suit symbols, rather than figures in the profiles of the other players, means that you have only an approximation of the PPI figures for these other players. However, there are examples at the end of this page showing what estimates can be made.

FREQUENTLY ASKED QUESTIONS

 

Will my PPI change by the same amount as that of my partner after a session together?

When you partner a particular player, your PPI will normally* go up or down by the same amount for the boards that you play together. However, there may be a difference of 0.1% shown on the profiles due to the fact that the calculations are made to more than one decimal place and the profiles show a rounded off figure.
Equally, if you have a good or a bad session, you may still find that your PPI does not change, even though the calculations have taken effect. For example, you may change from 51.06 to 51.14 and this will still show as 51.1 on your profile.
*The exception to “normally” is that if one player has played less than 600 qualifying boards or plays infrequently, or if one player but not their partner is a Club, their new results will have a higher weighting and their figures will go up or down by a greater amount.

Why won't my PPI change if a Guest Member is at the table?

The reason for this arrangement is that Guest Members are assigned an initial PPI figure of 50% and this figure may fluctuate somewhat over the first session or two as it settles to a reasonable figure. When guests are very new, they tend to play below their own standard while they are also concentrating on getting used to the unfamiliarity of playing online, and this would on the whole disadvantage a partner of the guest (and advantage opponents) and so that is why we don't count the scores. It is hoped that this in turn gives encouragement for players to partner Guest Members.

Is there not an advantage for regular partnerships?

Yes, there is, and this is considered to be the greatest shortcoming in the formula. It is currently thought that about 2% could be added to the figure of a member who plays mostly with pick-up partners for comparison with a member who plays mostly with a small number of regular partners. But the benefit varies from partnership to partnership and there is no way to include this in the calculations. In any case, we have no way to count how often a player has previously played with a particular partner, especially if a partnership plays face to face bridge together.
The other known factor that cannot be taken into account is if a player plays when unwell and unable to concentrate as well as normal on the game and thus a poor result on a day could be partly caused by external factors.

Where can I find PPI for each player?

You can find the PPI symbols of players by looking up their profiles. From the BCL Times, you can look up the Top 100 players by PPI, and this will show their PPI figures.

Can I opt out of the scheme?

No, but if you play in the Social or Coaching rooms, the PPI symbol on your profile is hidden for as long as you are in those rooms.

How does the effect of a board or a session that I play today diminish over a period of time?

The speed at which the effect of a past session diminishes will depend on how often and how many boards that you play every week or every month. The more you play, the faster it diminishes. The figures for the formula were selected such that for a reasonably, but not extremely, active player playing 416 qualifying boards in a three month period an effect of halving-every-three-months would hold true.
Thus the effect of a bad session would halve after 3 months and be a quarter after 6 months and be a sixteenth after a year and so what happens today has 16 times as much effect on your PPI as what happened a year ago, or 1024 times as much effect as what happened two and a half years ago. The effect of a bad session never goes absolutely to nothing but does tend towards zero fairly quickly.

Why do the PPI figures seem to be so sensitive, and why is so much weighting given to each board just played?

This is a relative matter. Because the figures are recalculated every time that you play, you can track small changes in your figure every day. It is expected that for most players, your PPI will tend to vary within a band of around 3 to 5% in the long term.
The weighting for each board (assuming you are a regular player) is such that each board that has just been played will account for a sixth of one percent of your figure, so a top or a bottom will increase or decrease your figure by approximately 0.08%. This may seem significant but it really isn't. Players should expect their figures to regularly go up or down by 2 or 3%. This is not a great movement given the wide spread of PPI figures that there is across the whole field of players. Any lesser weighting would not properly reflect current form.

I scored 55% yesterday, which is higher than my current PPI yet my PPI still went down

This can happen if you were playing with a strong partner or against weaker opponents than yourself.

My PPI is displayed as 51.0% but why am I still shown as a diamond?

PPI’s are displayed to one decimal point (although they are calculated to five decimal points). That you are still shown as a diamond means your actual PPI is between 50.95% and 50.99% and the figure has been rounded up in the display.

I was partnering a “Spade” last night, but he/she didn’t seem to play at a level that I would have expected of a “Spade”.

The PPI’s are indicative of a player’s results. It could be that your partner was having an off-day, or that you did not gel as a partnership.

Do I need to play with different partners to have an accurate PPI?

Imagine if both you and your partner have never played except with each other. You would have identical PPI’s, even though one of you may be better than the other. If just one of you partners other members, even if just occasionally, this will allow a representative differential to develop between your PPI and your regular partner’s PPI.
If you have an exclusive or nearly exclusive partnership with just one partner, it is possible that a differential in PPI that was established years ago has remained while the standard of the two members of the partnership have become closer together. The EBU NGS has recognised this phenomenon and has a method to draw the grades closer together. There is no provision in the PPI scheme for this, as only a very tiny number of players is ever likely to be affected, but adjustments can be made on a case by case basis. Please contact Barrie Partridge at Barrie@bridgeclublive.com if you think you may be affected by this phenomenon.

Do I need to play against opponents of different abilities?

No. The only advice to be given regarding selection of opponents is to not select the same pair of opponents every single day to the exclusion of any other players, and you can’t do that playing in DIDO mode anyway.

Why does my PPI rise in small amounts and fall in large amounts?

This is more likely to be a perception rather than reality. However, a possible reason may be that you were unwell or particularly distracted during a particular session.

Is it possible to have my PPI reset to 50%?

No. The idea is without merit, as your PPI would very quickly return to its present level, and so it is BCL policy not to reset PPIs.
Where can I read more about the PPI scheme?
The EBU National Grading Scheme (NGS) is based upon our PPI scheme, though it is more complex. Nevertheless, some FAQs in the Full NGS guide on the EBU web site are equally applicable to the PPI scheme, particularly FAQs 8, 14, 22, 28 and 37, and Further Reading sections FRs 1, 2 , 5, 13, 15 and 18.

Examples of how to estimate PPI changes

I am a frequent player and I have played over 600 boards and my PPI is 47%. I have just played some boards in DIDO with different partners. How can I forecast my PPI change for when the event becomes archived?

We first need to work out the average PPIs of (1) your partners (which we will call “b”), and (2) your opponents (which we will call “c”). You will need to have noted all their suit symbols.
I recommend you assume 44% for a “Club”, 48.5% for a “Diamond”, 53% for a “Heart” and 56% for “Spades” that do not appear in the Top 100 ladder.
We will call our own PPI “a”, the number of boards we have played “n”, and we will call our session % Match Points “p”.
We will also need to know our value for “m”, which will often be 600 but will be less for less frequent players who would need to check the formula in the main text.
Our change in PPI will be approximately n [p – {(a+b-2c)/2 + 50}] / m
So let’s say I played 20 boards, my PPI is 47%, My “m” is 600, my partners were all diamonds and my opponents were 3 “Clubs”, 4 “Diamonds” 2 “Hearts”, and a “Spade” with a 58% PPI, and I scored 44% over the 20 boards.
b = 48.5
c = [3x44 + 4x48.5 + 2x53 + 58] / 10 = 49
Change in PPI = 20 x [44 – {(47 + 48.5 – 2x49) +50}] / 600 = -0.117%
For our PPI not to change, we would have needed on this occasion
p = {(a+b-2c)/2 + 50} = 47.5%

I played just one board and scored 100% on the board. How will that affect my PPI if all the other players at the table had the same PPI as me.

If all the players have the same PPI, then (a+b-c-d) = 0 {(a+b-c-d)/2 + 50} = 50 p = 100 [ p – {(a+b-c-d)/2 + 50}] = 50 The sum of this over 1 board = 50
(a) For a frequent player who has played more than 600 qualifying boards altogether, m=600
New PPI is an increase of 50/600% = 0.083% over previous PPI.
(b) For an infrequent player who has played more than 300 qualifying boards altogether, but less than 150 such boards in the last 90 days, m=300
New PPI is an increase of 50/300% = 0.167% over previous PPI.
(c) For a newcomer who has played just 100 qualifying boards altogether, m=100
New PPI is an increase of 50/100% = 0.50% over previous PPI.


Page last updated on 10 December 2014

 

 

 

 

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