Examples of Ratings ( PPI)
I am a frequent player and I have played over 600 boards and
my PPI is 45%. I have just played 20 boards with a partner who
is a “Diamond”, and our opponents were a “Heart” and
a “Spade” respectively. How would my PPI change if
we had scored (a) 40%, (b) 50%, (c) 60% overall against this pair?
The range of PPI for a “Diamond” is 46% to 51%, so we
will assume his figure as 49%.
The range of PPI for a “Heart” is 51% to 55%, so
we will assume his figure as 53%.
The range of PPI for a “Spade” is 55% and over.
However, we will assume that his name does not appear in the Top
100 listing, so it will not be greater than about 58.5%, so we will
assume a rough average between 55% and 58.5% of 56.5%.
Had the example included a “Club” player, it would
be reasonable to assume a figure of 45%
For each board, (a+b-c-d) is 45+49-53-56.5%, which is –15.5%
And so, {(a+b-c-d)/2 + 50} = 42.25%
It is a reasonable approximation to assume that for each board, you
score the same % that is your overall % for the event.
(a)
For each board, p is on average 40%.
[ p – {(a+b-c-d)/2 + 50}] = -2.25%
The sum of this over 20 boards = 45%
m = 600
New PPI = 45 – 45/600 = 44.925%
(b)
For each board, p is on average 50%.
[ p – {(a+b-c-d)/2 + 50}] = 7.75%
The sum of this over 20 boards = 155%
m = 600
New PPI = 45 + 155/600 = 45.258%
(c)
For each board, p is on average 60%.
[ p – {(a+b-c-d)/2 + 50}] = 17.75%
The sum of this over 20 boards = 355%
m = 600
New PPI = 45 + 355/600 = 45.592%
On your profile, you see your PPI expressed to one decimal place.
Thus, for (a), you might expect to see a 0.1% drop in PPI on your
profile, for (b), you would expect a rise of 0.2 or 0.3%, and for (c),
you would expect a rise of 0.6%, but possibly only 0.5%.
How can I work out, as I start to play, what average % score
I need to achieve in order to maintain my PPI at its present level?
This can be calculated if you know the PPI figures of the other
players at the table and can work out {(a+b-c-d)/2+50}
In the above example, this figure was 42.25%
This is the average % score you need to achieve to maintain your PPI
at its present level, and if you score better, it will increase, and
if you score worse, it will fall.
In other words, it’s 50% plus the average of partner’s
and your PPI figures minus the average of the opponents’ PPI
figures.
With a strong partner and weak opponents, you may need to score 60
or 65% on average per board to maintain your PPI figure, while with
a weak partner and strong opponents, you may be able to maintain your
PPI figure just by scoring as little as 35 or 40% on average per
board.
In short, the system is designed so that it doesn’t matter
who the other three players are at the table with you, because the
factors of their strengths are taken into account.
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 (a) I am a frequent player and (b)
if I am an infrequent player, and (c) if I am fairly new and I have
only played 100 boards altogether previously.
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.
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, 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 I am partnering a Guest
Member?
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 of Full Members who
partner Guest Members. It is hoped that this in turn gives encouragement
for players to partner Guest Members.
Conversely, if you are playing against newcomers, in the long term
this should be of a small advantage, even though, occasionally, you
may find that the newcomer is a top class bridge player. Thus it has
been left that if you play against a newcomer, the boards will count
towards your PPI.
Is there not an advantage for regular partnerships?
Yes,
there is, and this is considered to be the greatest shortcoming in
the formula. A modification may be made in the future to attempt to
compensate for the slight advantage enjoyed by a regular partnership
over a pick-up partnership. Any modification will need to be empirical
and based on judgement. 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.
A further difficulty is that although we may find ways of counting
how often a player has previously played with a particular partner
for qualifying boards, and even counting boards played in other rooms
as well, it can't count boards played by a partnership at face to face
bridge.
The other known factor that is not 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. On
the profiles menu, 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.
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.
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 score reset to 50%?
No. The idea was briefly considered on one occasion, but the idea is
without merit, as your PPI would very quickly return to its present
level. Much resetting would also result in the average PPI moving
away from near 50%.
page last updated on
February 20, 2009
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