Full Overview of Past Performance Indicators (PPI) - (or ratings)

When you play a board, your PPI may or may not change depending on:

1) are you playing in a room that affects PPI?

2) What is your expected score based on the PPI of the four players at the table?

3) what is your actual score?

For an up-to date listing of which rooms affect PPI, take a look at “Bridge Rooms Timetable”.

Introduction

Newcomers are assigned an initial PPI of 50%.

For the same reason, your PPI will be seen only after you have played at least 50 qualifying boards

For the calculations, we need to know how many boards had previously been played by each player since the start of the scheme within the qualifying MP rooms only. The start of the scheme was the beginning of July 2002. We also need to know how many qualifying boards have been played by each player 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

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 partnering Guest Members).

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 partnering Guest Members). - 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 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.

FOLLOWING YOUR PPI

Unfortunately, it is difficult for members to keep an accurate manual check on the calculations of their PPI figure. This is because of the following factors:

PPI figures are recalculated after an event at the time the event is archived rather than when the event is scored.
The timings of this vary.
Most events are archived very quickly, but calculations for some tournaments are made sometime after the event.

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.

We provide a detailed GRAPH of your own PPI over time which can be accessed by opening your own profile and clicking on the actual % showing alongside your PPI symbol.

ADDENDUM ( May 30, 2009)

Update July 3rd 2009 - We are continuing the experiment until further notice - click here for a news item.

We are experimenting with increasing the volatility ( reducing the smoothing - the factor "m" in the equation) in the PPI formula as noted above, following our annual survey where we noted an overwhelming sense of difficulty in perception by CLUB rated players that it was difficult to rise above this level (The threshold is 46%). We have therefore increased the volatility by 10x of each of your most recent boards so that the smoothing factor is 1/10th the current setting (which varies between 30 and 600 according to the exisiting criteria used in the current formula) for each player who is below 46%. This will have the effect of enabling a session of good hands to rise your PPI dramatically, and in some cases, move into the DIAMOND area, where immediately the calculation will revert to the normal smoothing. Conversely, a few bad boards will drop your PPI just as dramatically. So during the month of JUNE 2009, do not be alarmed at this effect whilst we gather data as to the best settings for this change.

page last updated on July 3, 2009