Please accept my apologies if this question has been answered elsewhere.
I know this sounds stupid, but how is the opponent's average rating that appears on one's profile page calculated? I ask because I have just won two games that should have raised my opponents average rating 1 point but the average did not change.
Average rating of opponent calculation
-
slowblunder
- Posts: 77
- Joined: Thu Aug 04, 2005 4:23 pm
One possibility
Maybe it is a rounding problem.
1) Rounding up (0.5 to 0.9) and down (0.1 to 0.4):
Average rating before: 2000,5 exactly show 2001.
Then +0,9 because of the two games: 2001,4 exactly show 2001 as well.
2) Rounding by cutting the decimals:
Average rating before: 2000,0 exactly show 2000.
Then +0,9 because of the two games: 2000,9 exactly still show 2000.
Just my guess, very hard to tell unless all opponents´ratings are calculated in detail (which is very time-consuming depending on one´s number of games).
1) Rounding up (0.5 to 0.9) and down (0.1 to 0.4):
Average rating before: 2000,5 exactly show 2001.
Then +0,9 because of the two games: 2001,4 exactly show 2001 as well.
2) Rounding by cutting the decimals:
Average rating before: 2000,0 exactly show 2000.
Then +0,9 because of the two games: 2000,9 exactly still show 2000.
Just my guess, very hard to tell unless all opponents´ratings are calculated in detail (which is very time-consuming depending on one´s number of games).
Actually, it is not a rounding problem. The two games would have definitely moved up the opponents average rating by more than a point. I have played 263 games, and the difference between my two most recent opponent's ratings and my opponent's average rating was greater than 263.
I sense the calculation simply uses the average rating, mulitplies it by the number of games, and then adds the rating of your most recently completed games to that total and divides this total by the new number of games completed. If this increases the average by less than .5, then you do not gain a point. Fractions are essentially lost by this method.
Thus, if I have an average opponents rating of 1000 over 10 games, and I finish a game against someone with a 1005 rating, since this is not enough to bump up the average to 1000.5, my average opponent rating stays at 1000. So far so good, but I suspect what happens is that the next time I finish a game, it calculates my average assuming all of my games were against 1000 rated opponents; that is, it drops the extra 5 points.
To put it more simply, it does not keep track of fractions after each game is finished.
I sense the calculation simply uses the average rating, mulitplies it by the number of games, and then adds the rating of your most recently completed games to that total and divides this total by the new number of games completed. If this increases the average by less than .5, then you do not gain a point. Fractions are essentially lost by this method.
Thus, if I have an average opponents rating of 1000 over 10 games, and I finish a game against someone with a 1005 rating, since this is not enough to bump up the average to 1000.5, my average opponent rating stays at 1000. So far so good, but I suspect what happens is that the next time I finish a game, it calculates my average assuming all of my games were against 1000 rated opponents; that is, it drops the extra 5 points.
To put it more simply, it does not keep track of fractions after each game is finished.
-
gmiller
- Site Admin
- Posts: 1388
- Joined: Sun Mar 14, 1999 11:13 am
- Location: Jeffersonville, IN
- Contact:
You are correct, fractions aren't carried over. The primary purpose of this field is that it's used to calculate provisional ratings, and it works fine when the total number of games played is small. Of course, after you've completed a thousand games, then this field will probably never change again. So I guess I need to add in more accuracy.
Greg Miller