SmartPref Pro blog

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s Feb 1

How is the preferans rating calculated?

At first I looked into how Elo rating system is applicable to preferans. But it turned out that taking numbers of whists scores into account is a bit tricky and system requires certain preferans specific modifications. So I had to come up with nice fitting formula that is a bit simpler than Elo system but can take resulting scores in account.

The idea of formula is that your rating delta depends on other players rating, on number of whists you gained and on number of played deals during the game. To ease the delta, and not allowing it to sway too high there is a normalization coefficient that requires at least 200 deals to be played to get trusted rating.

You can play with it here.
I added some comments to the code (in English), you can just use different variants for initial variables and press «Build and run» to see how simulation works.

Note that user rating will never decrease and will result into no change if game turned for user as a total failure, otherwise it will increase by 1 or more, depending on gained whists. Even if player whist scores are negative there is a chance that rating still will increase if it is lower than average table rating.