Rating Dynamics: how they are calculated
How are dynamic ratings calculated for a specific match?
In matches where all players on the court have previous ratings, the procedure is as follows
1. The system looks up the current dynamic rating of each player in the match.
2. The system takes from a table the likely score of the match based on the current dynamics of the players/teams.
3. The system compares the likely match score with the actual match score. For example, if one player/team has a tenth of a point higher rating than the opponent, the likely score is 6-4, 6-4.
a. If the stronger team wins by a larger than expected margin, each player’s rating is increased based on the margin of victory and each losing player’s rating is decreased by the same amount.
b. If the stronger team wins by less than the expected margin, their ratings will actually decrease and the losing team’s ratings will increase.
c. Likewise, if the team considered weaker wins, their ratings will increase markedly and the ratings of the team which was favored would decrease by the same amount.
4. The rating obtained for each player in Step #3 is averaged with a maximum of their previous three dynamic ratings and that number becomes their new current dynamic rating. (Indirectly this connects the current dynamic to all previous matches but weights the four most recent matches more heavily.) The reason for this averaging is to even out the ratings in cases where some unusual situation causes an atypical result.
Each player rating is maintained in the system to the nearest hundredth of a point.
The difference in ratings of the two members of a doubles team is held constant in a calculation of an individual match. If the two players are three hundredths (.03) of a point apart going into the match then they are three hundredths (.03) apart after the calculation in Step #4. However, once that number is averaged with the three previous dynamic ratings (Step #5) that difference may change. This is how we measure the performance of players as they change partners.
Ratings for new players without a current dynamic are computed by several different algorithms depending on how many matches they have played against players who do have a current dynamic rating
1. The very first dynamic rating of a singles player is calculated using the rating of his/her opponent and the closeness of the match. This rating can possibly be a strike* if it is a significant win over a player in the upper part of the level. The rating system does not differentiate between singles and doubles rating so in rare instances a person whose rating is primarily derived from doubles may contribute to a rating for a new singles player.
2. The second dynamic rating is calculated using the rating of his/her opponent and the closeness of the match. It is also possible that this rating can be an immediate strike.
3. The third dynamic rating is calculated by a slightly different method. It averages the two existing dynamics together and compares them to the rating of the opponent. Then it looks at the closeness of the match to see if it agrees with the compared ratings. On the basis of that, the rating of the new player is calculated. It may be slightly higher or slightly lower than the average of the two previous dynamics.
4. The fourth dynamic is calculated like the third but all three previous dynamics are averaged together first. That average value is compared with the rating of the opponent and the closeness of the score. On the basis of that, another new rating for the player is calculated. But this time the rating from this match is averaged with the three previous ratings and that value becomes the fourth dynamic.
5. From this point on, the rating of the player is always their most recent dynamic. This value is compared to the rating of the opponent and the score, and a rating for the match is calculated. As in the previous step, this rating for the match is averaged with the previous three dynamics and becomes the next dynamic.
* A strike is a dynamic rating value which places a player significantly into the next higher rating level. Typically these players with strikes will have competitive (close) match scores with nearly any player at the higher level.