The power ranking is aimed to provide a somewhat scientific measure of players' current form. This is achieved by putting more weight on a player's performance in more recent tournaments.
A player's power ranking is based on that player's performance in the last four tour-level tournaments that player competed in. For each of those four tournaments, the ranking points (n1,n2,n3,n4) and the number of weeks (w1,w2,w3,w4) between the start of that tournament and the current week are recorded.
[Only players with total ranking points (n1+n2+n3+n4) more than or equal to 450 for men or 550 for women qualify for the power ranking. Note: 1. If the number of qualified players is less than 15, the points for qualification may be lowered. 2. If a male player makes to the quarterfinals of a Grand Slam, the semifinals of a Masters 1000, the final of a 500 event or wins the title of a 250 event, then he automatically qualifies for the power ranking. 3. If a female player makes to the quarterfinals of a Grand Slam, the semifinals of a Premier Mandatory or Premier 5, the final of a Premier event or wins the title of a International event, then she automatically qualifies for the power ranking.]
The power ranking points for that player is then calculated as follows:
For a Grand Slam, the number of weeks is adjusted by one (-1) due to the fact that Grand Slams are two-week tournaments. The same also applies to the BNP Paribas Open (Indian Wells) and the Sony Ericsson Open (Miami), though technically they are one-and-a-half-week tournaments.
[Note that a player's participation in Davis Cup or Fed Cup is not taken into consideration for the power ranking. And players absent from the tour for the past eight weeks automatically disqualify for the power ranking.]
On Monday of every week, up to 15 players each for the ATP tour and the WTA tour are ranked. Players ranked outside of top ten are listed as OLI (Outside-Looking-In).
The following are two examples for the power ranking on Aug. 17th., 2009:
n1=180, w1=1 [Montreal];
n2=2000, w2=7(=8-1) [Wimbledon];
n3=2000, w3=11(=12-1) [Roland Garros];
n4=1000, w4=14 [Madrid];
Power ranking points: n=719;
n1=550, w1=1 [Cincinnati];
n2=60, w2=2 [Los Angeles];
n3=280, w3=4 [Portoroz];
n4=900, w4=7(=8-1) [Wimbledon];
Power ranking points: n=779.
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