In any particular backgammon match, it's always possible to say that the outcome was determined by luck, since if the dice had been different the winner might have lost.  However, it's not possible to say that about 100 matches between the same players; the better player should win the majority of games, because the dice WILL more or less even out over that span.

Andersp: If you win against someone who is 2200 it means... well, not much, since the BK rating formula is inaccurate for backgammon anyway !

AbigailII: Your logic is unfaulty ! However, things can be seen for another point of view : cubed backgammon IS backgammon, and single games are the degenerated case of matches to one point.
I take "degenerated" for its mathematical meaning, it is not supposed to be insulting to one-pointer lovers :-)

But of course you are basically right, there isn't a bigger difference between Triple and Single than between Cubed and Single.

Andersp: only if its against me .. ;)

Andersp:  I'm sure you are not stupid, just pretending to be ;-)

If I lose to a lower rated player, it may be that he or she played better than I on this occasion, or because the dice favored him or her.  Similarly, if I win a backgammon match, it may be because of the dice or because I played better.  In chess, it's almost always a matter of skill, though there can be occasions I am sure when a player with less overall chess playing ability outplays a better player. 

The point about backgammon is that the player is only partly in control, due to the random element.  Thus, a rating in backgammon is not so much a prediction about the outcome of a single match, as it is a prediction about the outcome of a large number of matches.  Given a sufficiently large sample, the luck factor will even out and the player with greater skill will win a majority of the games.

My BKR is the result of a mathematical formula being applied to the results of my games.  Some of those games were won or lost primarily on skill, others on luck.  I offer no conclusion as to the interpretation of the backgammon BKRs on this site.

I hope that clarifies it, in case you were not just pretending ;-)

Hrqls:   So if i win agains someone who has 2200+  thats luck...and if he wins its skill? right?

Andersp: reaching 2100+ can be done by luck, and with little games .. the more games you play and the higher the bkr .. the more skill should be involved .. i think ?

Hrqls:  Thank you :-)

joshi tm: they already did so ? hmm :(
but the same could be done in any tournament

(although in triple gammon you can do something more sophisticated, and very unsportsmanlike!, with 3 people, each player losing a backgammon to another player, giving each player 5 points for 2 games ... but lets suppose most people are fair and sporsmanlike enough so that not 3 players would conspire ? and if they did it could be caught easily ?)

alanback: I might be stupid but im not sure i understand your talk about unfair rating.  If you lose 12 points to a lower rated player its because he was lucky, but you have reached your BKR because of your skill, not luck?   am i correct?

Hrqls: The only problem I see is that players already lost giving points to their friends by resigning in a backgammon position, like in the European Song Contest.

alanback: i thought i would post the link to your tournament :)

Unrated Triple Gammon -- all players (up to 20)

Andersp:  Assuming that a rating system can be properly designed, why do dice games differ in that respect from pure strategy games?  I don't mind losing games per se, I just would like the risks and rewards to be in balance.

alanback: you are right .. i didnt think of that earlier .. the TTT i played before were always unrated (although i didnt like that then, but now i see a TTT will probably decrease the bkr more than normal single games would do .. at least if someone would want to win the TTT)

joining your TTT now .. although i dont mind if it would be rated .. i like to be in a TTT with 1 big section :)

To get off the soapbox, I thought it would be nice to have a discussion of Triple Backgammon strategy.  I have some thoughts and I'm sure others do to.

One observation that occurred to me is that, if you can imagine winning all your games in a tournament, you could do so and still not win the tournament.  This is fairly obvious if you think about the scoring system, but it makes the point fairly sharply that one should always be on the lookout for gammon opportunities, even at the risk of losing a single (or even a gammon).

alanback: But if we didnt have any rating then you and other "very good players" could play in all tourneys without any worries and not be forced to only play each other, wouldnt that be nice? :)

 Andersp:  I disagree.  As I stated earlier, backgammon is a skill game with a random component.  A rating system is appropriate in backgammon to measure the players' relative skill.  It just takes more games to establish a reliable indicator of skill because of the random factor.  There are rating systems that work very well on other sites, mostly based the granddaddy of them all, FIBS.  This is not to say the rating system here doesn't work, but it does have serious defects.  The problems pointed out by nabla and Abigailll are the most significant ones. 

alanback: shouldnt be any ratings at all in the dice games

joshi tm:  The question is not whether ratings are important; of course, they are not in any real sense.  However, the question here is, if there are to be ratings, should they operate logically and consistently, or illogically and capriciously?

AbigailII:  Correct.  Of course, the fact that the system has one flaw is not a persuasive argument in favor of a different flaw. And yes, these are only significant to one who cares about having a rating system that works.  Those of us who do care are apparently in the minority, and not represented at all in the management of the site. 

nabla: Triple gammon is not more a different game than backgammon as cubed backgammon is. And we don't have a different rating for them either.

joshi tm: That was the point of my last sentence. Some points of rating matter even less when one knows that every rating must be taken with a grain of salt. Or maybe they don't matter at all :-)

nabla: Don't panic. What actullay do twelve points of rating matter in one's life? It's Backgammon.

alanback: Ooops, you are darn right, for the rating system to take this type of tournament into account, a gammon should also multiply the rating won/loss by three !

Imho triple gammon is a different GAME than backgammon anyway, so it is probably recommended to make its tournaments unrated. Or create a different rating list for it...

All that is, if one really wants an accurate rating system for backgammon, as we have already seen that the current one isn't accurate anyway :-)

Having started a TG tournament, I remember the other reason I don't like rated play.  The games are treated for BKR purposes just like any other game, but the strategy is different.  Whereas a gammon makes no difference in a standard one-point game, the whole point of TG is to play for gammons.  Therefore, a player will be willing to lose two games out of three if he can get a gammon in the third.  This will cause his BKR to decline, if he plays the optimal TG strategy.

My unrated TG tourney is still open for entries, and now is a single section of 20 players ;-)

lovelysharon: there is a green text underneath the gameboard now telling you that its a triple gammon tournament

play just started in a triple gammon tourny in one fellowship i belong to .. I notice there is no distinction between these games and regular backgammon games.. .. even as far as game type it says backgammon.. no mention that it is triple game.. ... strategy for these games are different .. is there anyway that they can be marked.. ??..

sorry .. it seems i posted the dutch link to the tournament

here is the english one : Triple Gammon

nabla: This is a very interesting discussion. I have recently felt that my BKR quite exaggerates my actual skill. Have usually have trouble with players rated above 2250 yet my rating has grown to >2300. I try to play multi-point matches with most players but often end up playing games with much lower ranked players (2000 - 2200). These games boost my BKR over time even though I'm not playing any better. Losses against similarly ranked player don't decrease my BKR significantly and so, my ranking continues to grow.

nabla:

This is not a phenomenon that is limited to games with a luck factor, however.
Yes, that was exactly my point, but I never manage to say things in a concise way !

I see now that you said that, I was focused on backgammon the first time I read it :-)

nabla:  LOL -- correct!

Turning back to the BKR issue, I think also that the phenomenon you pointed out probably explains why ratings don't appear to tend to an average.  I play mostly multiple point games, so the BKR adjustments are closer to what they "should" be than if I played single games.

alanback:
This is not a phenomenon that is limited to games with a luck factor, however.
Yes, that was exactly my point, but I never manage to say things in a concise way !

alanback: By the way, a heavier object does fall faster than a lighter one of the same shape, because the force caused by the air friction does not depend of the mass. Air friction is not something you want to factor out when you are a paratrooper ;-)

nabla:  You may be right.  Each match length has its own probability distribution.  If the match length is sufficiently high, then the probability of my winning might actually exceed the probability that is implicit in the BKR adjustments.  This is not a phenomenon that is limited to games with a luck factor, however.  

alanback: I thought I was describing your very problem, that if you play single games against a lot of lower rated players you will lose a lot of BKR points. If you were to play 21-points matches against the same bunch of players, you would probably take #1 position in the BKR list :-)

nabla:  I think that what you are describing is an independent phenomenon, which I did not mention for political reasons.    However, it actually should mitigate somewhat the phenomenon I described, because in a longer match the effect of luck is reduced.

Some of the mathematical discussion around BKR produces results that some may find counter-intuitive.  Although I believe strongly in intuition, some things we believe intuitively are just wrong.  This thought reminded me of a conversation I overheard on an airplane the other day.

One man was describing to another his experiences as a paratrooper.  He noted that he jumped with about 100 pounds of gear.  The other man exclaimed, "Well, you must have fallen really fast then!"

After a moment's reflection, I thought of Galileo's famous experiment dropping metal balls from the Tower of Pisa.  His great discovery was that the force of gravity produces a constant acceleration regardless of the mass of a falling object.  This led me to conclude that the listener's intuitive response was incorrect.

Then it occurred to me that my own intuition had failed me because I jumped (no pun intended) to the conclusion that a parachuter's rate of descent is independent of mass based on Galileo's experiment.  It turns out that the rate of descent is proportional to the square root of the mass of the parachute and its load. 

http://www.pcprg.com/rounddes.htm

I guess the lesson is that an ounce of experience is worth a pound of intuition and logic.

coan.net: It is very true that the BKR system is not accurate when applied to backgammon, but it is a common mistake to think that it is because of the luck factor. In fact, as alanback stated, it is because of the multi-game matches (cubed or not) that are counted like if they were one game.

There is no such thing as an absolute measure for skill. What the rating system can calculate is the "winning expectation", and that defines the skill difference. If I win more than 50% of the games against someone, then I am defined as stronger. If I win 90% of the games, I am defined as much stronger.

Now, and in a non quantifiable way, in some games the weaker player has more chances to win ; but these are not necessarily the ones where pure luck (e.g. dices) are involved. These are usually the short games, and the games that have a lot of forced moves. Less moves to think about mean less occasion to make mistakes for the weaker player. Of course the luck factor plays a role too, but it is one factor amongst others.

What will happen in games which offer good chances to the lesser player is not that ratings will be inaccurate, but that the rating scale will be shrinked. For instance, instead of scaling for 400 BKR to 2400 BKR, it could scale from 1200 BKR to 1600 BKR. The only undesirable effect is that as one game still carries the same BKR change, there will be more variation of the positions of the players. E.g., if I lose 10 points, I will lose 10 positions in the ranking list, because the players are all very close to each other.

If wished, this can be corrected as there is a "rating scale" constant in the BKR formula. But you can see that it is definitely not the problem in backgammon, where top players do have a lot more than 1600 BKR !

The real problem in backgammon is that matches count the same as single games. But if player A beats player B 60% of the time in single games, he may beat him 90% of the time in a 5-point match. Or whatever, I didn't do the math :-) Hence, rating-wise the matches favour the better player and the single games favour the lesser player. This is a real distorsion in the rating system, and you can indeed see that good players who play a lot of single games are considerably underrated - AlliumCepa comes to my mind, although he plays matches as well. On the other hand, people who play only matches are overrated. For example, me (but not for rating reasons, I just don't like playing without the cube).

The good news is that one knows a very simple way to adjust the BKR formula in order to take the length of the match into account. Basically, in a n-length match, one should just multiply the rating difference by the square root of n. As you can notice, this changes nothing to the way single games are counted.

This is not a specific backgammon formula, because it is not perfect for taking cubed matches into account, but perfect for taking "first to n points" matches of any game into account. In fact it should be applied to all games. If I start a rated 10-games chess match against a lower rated player, I am just getting some undue rating points. Of course, this is much more often done in backgammon than in chess, because the doubling cube can be used only in matches.

The bad news is that I told Fencer about that quite some time ago and while he didn't say no, he did not sound too hot about updating the rating system. Indeed I understand pretty well there are more important issues to settle first. After all, rating are just numbers, what is important here are the games !

Moreover, if there were 63 games rather than 7, the problem could actually be worse.  This is because the BKR system as it presently is implemented will predictably drive my rating downward if I play a large number of games against lower rated players.

For example, suppose that on average, I should win 65% of my games and receive +4 points for a win, -12 points for a loss as described below (the actual win/loss disparity is probably greater).  If I play 100 games and win 65 of them, I will receive 65 x +4 points = +260.  However, I will lose 35 x -12 points or -420.  Therefore, simply by winning the predicted number of games I lose 160 points!

In actuality, I would lose fewer points, because as time went on my rating would be lower and the adjustments would moderate.  However, the principle is still the same, which is that as long as I and my opponents play at our respective skill levels, my rating will fall simply because I play lower rated players.  This should not happen.  If my average winning chances are 65%, then wins and losses should produce point adjustments in a ratio of approximately 1:2 (e.g. +4, -8).

The objection may be raised that, under my standard for a fair system, players would not be able to rise and fall significantly in the rankings.  The answer to that is that players should not rise and fall unless their skill level changes.  Everyone starts at the same level, and moves to a certain rating according to his or her skill level.  After that, changes in ranking should occur only if players get better or worse at the game.

It seems that, under the BKR system in place today, if everyone were constantly playing everyone else, all players should tend toward some average BKR.  I guess the only reasons this does not occur are that (i) new players are constantly being introduced to the system, (ii) old players leave, and (iii) players tend to select opponents closer to their own level.

alanback: thanks!!! a real sportsman!

would it better or worse when there are more players per section ?

Andersp: yes .. its meant to be that way .. but unfortunaly thats not supported at the moment on brainking .. although fencer seems to have increased the possible maximum size of the sections

should i ask him to increase the number of players per sections ?

Andersp:  There is no such thing as a "correct" BKR; it is the result of a calculation.

coan.net:  Do you think that "very good players" (2300+) who never play lower rated players have a correct BKR? 

Andersp:  Unfortunately, there are only 8 players to a section. 

alanback:  But this tournament will probably have 64 players so a very good player like you shouldnt have bad luck in 63 games?

coan.net, fencer: http://www.fibs.com/ratings.html#explained

Andersp:  Backgammon is not a luck game; it is a skill game with a random component.  A large part of the skill in backgammon is understanding and working with the random component.  However, it frequently happens in a single game that luck overwhelms ths skill component, and a lower rated player wins because of having better dice rolls.  The chances of this happening diminish as the length of the match increases.  But in a single game, a very good player can expect to lose to an average player 25-35% of the time.  This would be unheard of in chess, on which the ratings system here is based.  

alanback: You know, Fencer has been doing different things - like AutoPass which seemed like something that we would not see on this site.

Maybe it's time to see if Fencer is interesting in putting in place different rating "systems" for different types of games.

- - - - -

For those of you new, the rating system that BrainKing uses is a type based on Chess rating system - a 100% skill game. A game where a 2000 rated players should beat a 1500 rated player 99% of the time.

For Backgammon (and other games with luck factors), I would say Backgammon is around 60-75% skill game with 25-40% luck (others would say higher & lower - but that is a stupid debate to have - but everyone agrees that there is more luck to it then say Chess). Anyway, a 2000 rated backgammon players should beat a 1500 rated players probable around 75% of the time. Since bad dice can come into play. A good player can still win with bad dice (that is where skill come into play.), but enough bad dice can doom even the best gammon player.

So there are certain Gammon rating systems out there, which in my opinion should be used for Gammon - and other games with luck factors (Battleboats, Dice Poker, etc...)

Fencer - any chance of having different rating systems for different games? I'm not sure of the formulas off-hand, but if you were interested, I'm sure someone can help you get the correct formulas and such.