Re: [pbmserv] General questions about ratings

[Richard Rognlie <rrognlie@gamerz.net>]

On Fri, Jul 15, 2005 at 04:47:57PM -0600, Robert Barrell wrote:
> A) Is there existing documentation for this so I may seek the answers 
> myself?  If so, where?  I couldn't find any.

http://www.gamerz.net/pbmserv/ratings.html

> B) Is the method the same for each type of game?  If not, what are the 
> differences?

Yes (for now).  We reserve the right to implement Game specific rating
schemes in the future (if I ever get off my duff and actually do it, I'll
add FIBS [First Internet Backgammon Server] style ratings to the backgammon
et al. engines.)

> C) At what rating does a newcomer start?

I think you start at 1600 and move up/down with a skew toward 1720 in your
first 20 games.

> D) How do wins, losses, and ties (respectively) affect rating?

Depends on how many games you've played, your rating and your opponents rating.

> E) How does the opponent's rating affect the rating after a particular game?

The theory is... if you beat someone who is rated below you, it's "expected"
and you don't game much.   You gain less the farther ahead of them you are
with some cut off point (719 point delta) where you no longer gain anything.

If you beat someone who is rated above you, that's an upset, and you gain
much more than you would for an expected win.   Again, there's a cap.

> F) How do a game's options affect the rating after that game?

For the most part, they don't.   but it depends on the game.

> G) How many games, wins, losses (or some combination) does it take to 
> move from "Provisional" to "Established"?  Are there other factors (e.g. 
> time)?

20

> H) Can an Established rating ever slip back to Provisional (e.g. not 
> playing a certain number of games - or at all - for a certain amount of 
> time)?

Nope.

> I) What else should one know about ratings that I haven't already asked?

While provisional, all bets are off.   There are times you can win a game
and yet lose points (to prevent someone from artificially getting a high 
rating by one fluke win against a strong opponent, and then a string of
wins against very weak ones)

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