Power Ratings Home Page

 

Bowling Average

 

            When I bowled, no one ever asked me what the total number of pins I knocked down was, but a lot of bowlers wanted to know what my average was.  Master Points is the total number of pins.  Power Ratings is the bowling average.

 

What is a Pair Rating

 

            Pair Ratings are the strongest rating for a partnership.  It is the pair’s average game percentage adjusted by their degree of difficulty.

 

What is a Degree of Difficulty (DOD)

 

            Add up the PR’s for all of your competitors (the players sitting your direction in your section and other sections if scoring across the field) during the past 24 months and divide by the total number of competitors. Subtract 50 from this result to find your DOD.  Let’s say that your average competitor has a PR of 52, and you and your average partner have an average game percentage of 51%.  You must be a little better than your competition that has a PR of 52.  So add your DOD, 2, to your average game percentage, 51, to get a PR of 53 for you and your average partner.

 

What is a Power Rating (PR)

 

            PR is your average game % when you are your own partner and you compete against average players.

 

            A PR may or may not be a measure of your bridge ability or level of expertise.  It is always a measure of your average level of play.  A player may or may not play at the same level in the finals of the Blue Ribbon pairs as when he or she goes to the club to have a relaxing evening of entertainment.

 

Somewhat simple explanation:

 

            Every match point game you play has a final game percentage.  The game % for each game is a combination of your game % and your partner’s game %.  If you and your partner are equally strong, your game % is ½.  Otherwise the game % is split in proportion to your and your partner’s strength, the stronger partner getting the larger share.  All of your game %’s during the past 24 months are averaged to give you ½ of your PR.

 

Where does a PR come from?

 

            Since your PR is your average game % against average competition, your actual average game % is adjusted to show what it would be against average competition.  DOD is this adjustment.

 

            Your adjusted average game % is a combination of ½ of your PR (Self) and ½ of your average partner’s PR (Part).

 

            If you play 10 games with Partner A, 100 games with partner B and 1 game with partner C, multiple A’s PR by 10, B’s PR by 100, and C’s PR by 1.  Add these results together and divide by 111 to get your average partner’s PR.

 

            Self + Part = % + DOD

 

            This is the formula used to prove that the correct Power Ratings have been found.

 

            At this point you are thinking that all PR’s must be known before any PR can be found.  That is correct.  There is no formula for finding PR’s.  I use the power of the computer to do this.  I make educated

guesses for everyone’s PR then use the formula to see if the guesses are correct.  If not, I guess again.

 

            While everyone has a PR, (I need this to calculate DOD), only players who meet the minimum requirements are considered rated and can be found in the Power Rating leader tables.  You need 11 games with

rated partners other than your favorite partner, (the rated partner you have the most games with).  If you only have one partner, there is no way to tell who the stronger player is.

 

Possible Power Rate Distortions

 

            Lucky and unlucky games, with occasional partners, can distort a player’s PR, especially when a player plays more than 2/3’s of his games with the same partner.  The two partners PR’s will fluctuate up and

down in opposite directions of each other.  To minimize this, all of each player’s PR’s during the past 24 months are averaged.  The actual (top) PR is this average.  The (bottom) average of the SELF column is ½ of the

current month’s calculated PR.

 

Example of Self Rating calculation

 

               I play 11 games with John Doe. We average 50%.  I play 11 games with Jane Doe. We average 55%.  What does this tell me about my power rating?  Nothing, but it does tell me that Jane Doe has a higher self rating than John.  Jane has a self rating 5 points higher than John.  Jane and John play 11 games with each other and they average 60%.   Now we all become rated players.  To become a rated player you need 12 games with other rated players.  11 of those games need to be with rated players other than your favorite rated partner, the rated partner you play the most games with.  The only way to become a rated player with only 12 games is to play one game with each of 12 different rated players.  The self ratings are calculated as follows:


­___________________________________________________________________________
!  John                 !   Jane                 !   Me                   !
!                       !                        !                        !
!       32.5 Jane 60%   !        27.5 John 60%   !        27.5 John 50%   !
!       22.5 Me   50%   !        22.5 Me   55%   !        32.5 Jane 55%   !
!                       !                        !                        !
!27.5   27.5      55%   ! 32.5   25        57.5% ! 22.5   30        52.5% !

John's average game percentage is 55%.  He averages 60% with Jane and 50% with Me.

John has a rating of 27.5, lower left number, left box.
Jane has a rating of 32.5 and I have a rating of 22.5 (2nd column, left box)

John's partners have ratings of 32.5(Jane) and 22.5(Me)
John's average partner has a rating of 27.5
John's rating 27.5 and John's partner's average ratings 27.5 equal John's average game percentage, 55%

Jane's average game percentage is 57.5%.  She averages 60% with John and 55% with Me.

Jane has a rating of 32.5, lower left number, center box
John has a rating of 27.5 and I have a rating of 22.5 (2nd column, center box)

Jane's partners have ratings of 27.5(John) and 22.5(Me)
Jane's average partner has a rating of 25
Jane's rating 32.5 and Jane's partner's average ratings 25 equal Jane's average game percentage, 57.5%

 

This example assumes that all opponents are dead average.  DOD = 0.

 

I did not calculate the above ratings (27.5 32.5 & 22.5).  I applied different self ratings to the formula, your self rating plus the average of your partner’s self ratings equals your average game percentage, until all the equations were correct.

 

Power ratings assume that everyone has an average level of play and over the long run their scores reflect that average level of play.  But this is real world.  Some players make more mistakes with some partners than with others.  Power ratings can not tell if your partner is making more mistakes, you are making more mistakes, or a combination of both.  I doubt that any rating system, including Master Points, and Lehman Ratings which are found on OKBridge, will ever figure that one out.  When power ratings see bad results, it assigns lower ratings to both partners.  You can see where this is happening by looking at your personal summary.

 

Under “Unit Races” on the home page, select “Other Units”.  Then select your unit.  Now you will be in your Unit’s home page. Select “Power Ratings” and you will be taken to your Unit’s Power Ratings leader board.  If there is a yellow box at the top of the leader board, you may be able to find your name.  If your name is not listed, contact me at ckchampion@netzero.net, and I will be happy to add your name.  After you select your name you will see your summary.  The left side of the screen shows a summary of your partners during the past 24 months.  Your games with the partners near the top of the page have exceeded your and your partner’s power ratings.  Your average game percentage with that partner has been divided between you and your partner using a ratio equal to your and your partner’s overall power ratings.  The partners near the bottom, well someone, you or your partner, has not been playing up to their average level of play.  It is no prediction of your future games, just a recap of what has happened during the past 24 months.  The right side of your summary is devoted to individual games played during the past 4 months. 

 

Power ratings measures one attribute of each player, his or her expertise at the bridge table. Master Points measures 4 attributes. (1) a bridge player’s expertise. (2) a bridge player’s partner’s expertise. (3) a bridge player’s opponent’s expertise. (4) How many ACBL sanctioned games a bridge played has competed in.  Power Ratings looks only at a bridge player’s average game percentage over the last two years. The number of games played is not considered. This system calculates the player’s opponent’s average rating for each and every game. The player’s game percentage is adjusted up or down according to how much the opponents are above or below average. This eliminates the opponent’s expertise. This system subtracts the partner’s rating from the player’s game percentage. This eliminates the partner’s expertise. The remaining percentage is the bridge player’s expertise, or "Power Rating".

 

Your game percentage (G%) for each and every game you play is divided into 3 parts.  Your contribution/Self Rating (self).  Your partners contribution/Self Rating (Part)  Your opponents contribution/ Self Rating (DOD).  The sum of the opponents sitting your way, N/S if you are sitting N/S, is averaged and the amount above or below the average pair (50) is your degree of difficulty (DOD).

            Self = G% + DOD - Part      or      Self + Part - DOD = G%

This is the basic formula used to prove everyone’s rating.  The program makes educated guesses then uses this formula to see if each guess/Self Rating is too high or too low.
Cycle 1: The program starts with a rating of 25 for all players. All DOD’s will be 0 and all partner ratings will be 25. Each player will get a new rating of Self = G% + 0 - 25. If your average game is 52% then your rating is 27. Since the new rating is different from the old rating, 25, then it is not correct and a new cycle needs to be run.
Cycle 2: The next cycle starts with 27 for you as well as new ratings for all other players. DOD’s for all games will be calculated and used to calculate new ratings. Let’s say your average DOD is 50.25 (.25 above average), average partner’s rating is 26, your average game is 52%. Self = 52 + .25 - 26. Your rating is now 26.25 which does not match your previous rating of 27. Not correct and a new cycle using a rating of 26.25 is run.  Many Cycles: Typically 12,000 cycles are needed to arrive at correct ratings for all players.

              

               Adjustments are made to recognize the difficulty of a partnership’s opponents. Since you are competing against the players sitting in your direction, N/S for example, the ratings for all the other N/S players are averaged together, to calculate how much higher or lower than average your N/S opponent is. This percent is then added or subtracted from your game percentage. If your opponents are experienced, your game percentage is adjusted upward. If your opponents are less experienced, well your game percentage adjusts down. Self + Part = G% + DOD.

 

Most underrated KO teams

 

               When I suspended KO Power Ratings, I tried replacing them with actual KO results.  This did not work because comparing the W/L record of teams in bracket 1 with teams in other brackets is like comparing apples and oranges.  Instead I chose to prove/disprove the validity of Power Ratings.  If teams flagged as underrated had W/L records both above and below 50%, then Power Ratings would fail as often as they worked.  The teams shown here are selected based on underrate (UR), not their W/L record.

               KO’s should be bracketed so that all teams in a bracket have about the same chance of winning.  This test is designed to show which teams win far more often than the average team, and which teams virtually never win their bracket.

 

Master Point to Power Ratings conversion chart

 

               This chart is the average Power Ratings for players in these Master Point ranges.  If you want the average Power Rating for 5000 Master Points, it is the low end of the Power Rating range corresponding to 5000 to 10000 Master Points.  For 7500 Master Points, the average Power Rating is the exact middle of the corresponding Power Rating range.

 

Games Stratified by Power Ratings

 

               The game files include Strats based on Pair Ratings first, Power Ratings second, Master Points last.  At the end of each line, the first character is the Strat assigned at game time.  The second character is the Strat assigned by Power Ratings.  The last number is the actual rating used to calculate the Power Rating Strat.  Strat A is the top 3rd of the field.  B middle 3rd. C bottom 3rd.  If a Pair Rating exists for that pair, it is used.  Otherwise each player’s Power Rating is used.  If a player has neither, then a Power Rating is computed using the Master Point to Power Rating conversion chart.

 

What is wrong with the Master Point rating system?

 

            Every time you play, your rating goes up or it stays the same, no matter how poorly you do.  Many members feel bridge players would object to seeing their rating go down.  Instead we insist that players play in the highest strat or bracket if they have that many Master Points.  They and their partners/teammates may feel they have very little chance of winning.  As a result, many of these players stop participating.  I feel it is better to lower their rating so they can play in a bracket or strat where they are competitive.  I think they will come back.

 

            I will not name these players, but I will name the players that are in the opposite position.  These players have a “level of play” that is higher than the top of their strat.  To see the players in your unit who play at a level higher than the top of their strat, click here and click on your unit.

 

            When stratifying events, Power Ratings will look at both players in a partnership.  If a Pair Rating is found, that is used.  If not, but Power Ratings are found, that is used.  If one or both partners have neither, then Master Points are used for the player(s) with no Power Rating.  Only players that rarely play will have neither.  The level of play for that partnership will determine the strat.

 

Tight brackets

 

            I often hear players say they like to play KO’s in Gatlinburg because the brackets are so tight.  The only thing tight about these brackets is the number of Master Points for team in a bracket.  The level of play can very widely within a bracket.  If KO’s were bracketed by Power Ratings, then all teams in a bracket would have about the same level of play, but their Master Point totals would very widely.

 

What is the purpose of Power Ratings?

 

               The Master Point Rating system is a great system for awarding exceptional play, but a poor rating system.  It should be renamed the Master Point Awards System.

 

               Power Ratings is a rating system based on a bridge player’s ability today.

 

               Bridge events should be bracketed/stratified so that all teams/pairs within a bracket/strat have close to the same skill level and chance of winning.

 

               We need to keep Master Points as rewards for winning events.  However using Master Points to push players into ever higher brackets/strats is a disincentive.  Better to use Master Points to measure a player’s ability during their bridge career, and use Power Ratings to measure a player’s ability today.

 

A rating system based on performance is a long way off.  Until then, Power Ratings is a tool to gage your chances of winning.  This is based on your performance compared to your Master Points.  Power Ratings will estimate you and your partner’s average game percentage.  You will need to supply the type of event you will play in.  Power Ratings will estimate your KO team’s won loss match percentage.  Click here:

 

 

PR Predicts

 

 

 

How Power Ratings protects your privacy

 

You can hide your personal summary.  Send me an email and I will send you a secret link to your Personal summary.  The game data used to compute Power Ratings is readily available on the internet.  If you want your name, and personal summary, removed from Power Ratings, I will be happy to do this.  Send me an email at ckchampion@netzero.net.

 

How to include your club games (club owners only)

 

·  You need ACBLscore. Almost all clubs use this to score their games.

 

  This looks daunting, but once you learn it, it will seem as easy as creating the monthly reports for the ACBL.

 

  1) start ACBLscor

  2) From the menu (top line) select "Utilities"

  3) Select "Backup/Restore"

  4) Select "2 Backup Game Files"

  5) Backup Location: "c:\acblscor\gamefile"

  6) Enter game files to backup.  Type in "1408??" for Aug, 2014 or "14????" for all of 2014 or"??????" for all games

 

  the file name will be 1408xx.lzh or 14xxxx.lzh or xxxxxx.lzh, and found in "c:\acblscor\gamefile"

 

  Please attach this file to an e-mail and send to me at

 

  ckchampion@netzero.net

 

I can use up to two years worth of games, but I will use any amount of games you send. I update each month. The best time to send me your new games is the same time you e_mail your reports to ACBL.

 

You are done, but if you need more help with browse buttons and attachments:

 

 

 

 

Browse button:

 

  1) From ACBLscor, after step 4 "2 Backup Game Files"

 

click on the browse button

 

Desktop is at the top.  Click on it.

 

  or

 

  You can expand a different location by clicking on the icon

to the left of the location.  You can continue expanding locations

within each location by clicking on the icon to the left of

the sub location.  For example "ACBLSCOR" and then "GAMEFILE".

When you find the location you want, click on it, not the icon to

the left, and click on the "OK" button.

 

 

 

 

  2) from your email account "attaching the backup gamefile"

 

select attach or attachments

 

you should see a browse button.  Click on it.

 

you should see a list of locations on the left.

 

  a) if you see "Desktop" and that is where you put the backup gamefile:

 

     click on it and find "1107XX.lzh" in the list on the right side.

     click on it and click on the "open" button or the "OK" button.

     click on "attach" and "finish" or whatever you have to do to

   complete the attachment process in your email account. 

     send email to me.

 

  b) if you do not see "Desktop" or you put the backup gamefile

somewhere else click on the "Folders" button

 

     Click on the icon to the left of "Desktop"

     Click on the icon to the left of "Computer"

     Click on the icon to the left of your hard drive "C:"

     Click on the icon to the left of your high level folder "ACBLSCOR"

     when you get to the last folder "GAMEFILE" click on it, not the icon

   to the left, and find  "1107XX.LZH" in the list of files on the right.

     Click on the "open" or "OK" button.

     click on "attach" and "finish" or whatever you have to do to

   complete the attachment process in your email account. 

     send email to me.

 

Any questions please contact me.

 

ckchampion@netzero.net

Chris