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Old 12-01-2012, 01:29 AM   #24
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Join Date: Jul 2008
Posts: 41

Here in Holland, we have a dynamic rating system that I tend to think is very good, and that combines the following three features:

(1) For any given match, the effects on players’ dynamic ratings are determined ONLY by which player wins the match; scoreline is irrelevant.

(2) However, the strength of the opposition in any given match IS taken into account. Basically, the extent to which your dynamic improves as a result of a match win depends upon the dynamic rating held by your opponent. Thus, to take an extreme example, if you manage to beat an opponent who has a far superior dynamic rating, then relatively speaking your dynamic rating improves a lot (and of course your opponent’s dynamic rating worsens a lot). And conversely, if you beat an opponent whose dynamic rating is far inferior to your own rating, then neither your own nor your opponent’s dynamic rating changes at all.

(3) The system is completely transparent and therefore predictable. That is to say, at any given moment you know your own dynamic rating, as well as your opponents’. Therefore, once you know who your next opponent is, you can easily calculate how winning – or losing – your next match will affect your dynamic rating.

Moreover, the results in this rating system actually make sense: it concurs with intuitions and reasonable expectations.

Let me give one numerical example.
Dynamic ratings basically vary between 1.000 and 9.000 (although slight overflows on both ends are possible), where 1.000 represents the BEST players and 9.000 the WORST players. And basically each player is given a ‘match result’ for each match he plays during the current season, and the dynamic rating of a player at any point during the season is simply the average over this year’s match results so far. (At the beginning of the year, each player gets six fictitious match results equal to his end year rating of the previous season; these fictitious match results are then erased one by one as they are replaced by real match results obtained in the current season).

Now let us assume player A has a dynamic rating of 5.2, whereas his opponent B has a dynamic rating of 5.8 (i.e., A is supposed to be the somewhat stronger player). The ‘match result’ for each player is then calculated as follows:

• The winner gets his opponent’s dynamic rating MINUS one.
• The loser gets his opponent’s dynamic rating PLUS one.

So in our example, if player A wins he gets a match result of 4.8, and the losing player B get a match result of 6.2. If B wins, however, then A’s match result is 6.8 and B’s match result is 4.2.
Note that in this example, as always (except for the caveat noted below), the winner’s dynamic rating improves as a result of winning, and the loser’s rating worsens. But also note that in the case of a “surprise result”, i.e. the player B with the inferior rating manages to win, the effects on both players’ ratings are greater as compared to the “expected result”.

This always works, except if the difference between the two players’ ratings is greater than 1, AND the better-rated player wins the match (as expected). In that scenario we cannot calculate the match results in the usual way, as it would imply that the winner’s rating would worsen and the loser’s rating would improve. But in that case the solution is simple: neither player’s rating changes! In other words, in such a case, neither player is assigned a ‘match result’ for that match.
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