How are the ISRs computed?
The basic idea is an iterative one. Begin with all teams set to an even rating — 100 in this case. Then, for each game played, give each team the value of their opponent’s rating plus or minus a factor for winning or losing the game — 25 in this case. Total all of a team’s results, divide by the number of games played, and that’s the end of a cycle. Then use those numbers as the start of the next cycle until you get the same results for each team for two consecutive cycles.
