When two teams play, each set (i.e., game) of the match is treated separately. The winning team's rating will increase and the losing team's rating will decrease, according to the following formulae:

Assume Team A beats Team B:

TeamA_New_Rating= TeamA_Old_Rating + (1- Probability_of_winning) * 32points
TeamB_New_Rating= TeamB_Old_Rating + Probability_of_winning * -32points

The probability of winning formula is calculated based upon the ratings:
Probability_TeamA_wins = 1/(1+(10^-((TeamA-TeamB)/400)))

For example, if Team A's rating is 1600 and Team B's rating is 1500 (and A beats B):

TeamA_New_Rating = 1600 + (1 - 1/(1+(10^-((1600-1500)/400)))) *32
= 1600 + (1 - 1/(1+(10^-(1/4)))) *32
= 1600 + (1 - 1/(1+(10^-(1/4)))) *32
= 1600 + (1 - 1/(1+.56)) *32
= 1600 + (1 - 1/(1+.56)) *32
= 1600 + (1 - .64) *32
= 1600 + 12
= 1612

The table below shows how ratings relate to probability of winning:

Maintained by Kevin M. Wendelboe office@CarolinaRegionVB.org

Last Updated: Tuesday, 15-Feb-2005 13:37 EDT