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Details on XBox TrueSkill Ranking System
rupert0 writes "A research paper on the Microsoft website gives an insight into the way that gamers will be ranked on the new-style Xbox Live. The paper outlines some existing ranking systems, as well." From the article: "The TrueSkill(TM) ranking system is a skill-based ranking system designed to overcome the limitations of existing ranking systems, and to ensure that interesting matches can be reliably arranged within a league. It uses a technique called Bayesian inference for ranking players. Rather than assuming a single fixed skill for each player, the system characterises its belief using a bell-curve belief distribution (also referred to as Gaussian) which is uniquely described by its mean (speak [mju:]) ("peak point") and standard deviation (speak [sigma])("spread")."
Given that the current system could be described as a "bubble sort".
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That is, the cheaters and glitchers bubble to the top, the people looking for a fair and fun game drop to the bottom and eventually give up and stop playing.
Karma: Chameleon (mostly due to the fact that you come and go).
...one must not be able to rank up with simple tactics.
You can hold down the "B" button for continuous firing.
Let me start this by saying I have no problem with the Bayesian framework... this usually can be a source for a fight in statistics departments ... I've seen a situation where a professor snapped a potential professor hire for his usage of the Bayesian framework in his presentation.
, j=1..n)... or in more typical terms of likelihood the posterior density (density shaped by events) is proportional to the likelihood times a "prior" belief, or distribution.
Typically the Elo system works on a iterative mechanism that updates after a match... that is to say that you have a prior rank, you play your game, and you have a post-match rank (not technical terms mind you) usually its R[player,after]=Rank[player,before]+("speed factor")(Result(0/1) - WinExpectancy(yourrank,theirrank). For Chess the logit function is used with some additional scaling factor (1/(1+exp(-(yours-theirs)/400)).
This new system is taking advantage of the Bayesian framework, for those not P(A[i]|B)=P(B|A[i])*P(A[i])/sum(P(B|A[j])*P(A[j])
What's the problem in this... the Elo system can adapt to change in ability of the player over time. A Bayes based system can't. The Bayes estimates converge to what is the true values of the parameters in the model as the number of samples increase to infinity. So an estimate given under frequentist frameworks (MLE, UMVUE, Method of Moments) converge to the same estimate given under Bayes frameworks (mode of the posterior, mean of the posterior). Your estimate can only become more refined with data... if you play enough games, the framework cannot account for any substantial changes in skill. The variance of your stregth or ability rating will decrease. Of course the property of the updating scheme is a nice one to have... I've got to figure there is some usage of approximations... they are very scant in terms of either a prior or a modeled distribution for the event (logit, probit, cloglog, some arbitrary cumulative density function). I'm not going to complain about the normality assumptions in prior or posterior though... I wouldn't know about this situation in particular but the Central Limit Theorem pops up over and over again in statistics (there is a Bayesian CLT but I don't know what that entails). Especially in linear model variants such as this. I see this more as improvement by obfuscation... throw out cute words like "True Skill" and the idea that you have this better system that people will impart its own hopes on it. So, if you want to game the system, just win a lot really early before your variance decreases... looking at the formulae there doesn't seem to be any indication that they are utilizing a conjugate prior (which can help for giving forms for solutions that will not want to eat your pets)... otherwise they'd be staring at a gigantic matrix... and anybody who has dealt with multiple parameters in this situation knows that there will be a correlation structure... which seems to be ignored in the formulae.
Most approaches I have seen thus far (as a second year grad student) in Bayes methods works away from a nice framework... many sound methods and realistic problems require Markov Chain Monte Carlo or similar techniques (which can be a nightmare in a computation sense)... either you have to have something of an incredibly nice form or you need to make use use of approximations to make a system like this work. I don't see how this will be all that appropriate in online gaming... sports I can see since you aren't taking somebody who mastered squash and putting them right into rugby. (Irrelevant to topic at hand-->) I've always had an interest in methods of ranking players/competitors but mainly from a sports angle. I've got a system drawn up in my head, its a matter of seeing if I can get it to work and then having a few hundred breaks work my way in terms of implementation (again, MCMC is probably the best tool in a lot of cases... but its a computational/time killer). The Bayesian framework is great if you have a good sense of piror belief as it can help guide you to a solution... but it is naturally biased (not necessarily from a point of malice) and at times it is used inappropriately.
Seriously, three Xbox 360 articles on the front page? There's astroturfing, and then there's Slashtroturfing. Give it a rest, guys. I mean, who gives a shit?
Gaming is an interesting phenomenon, and I follow the market and read Penny-Arcade--but I don't need to see all this advertising for Microsoft's next attempt to win another market.
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$tar -xvf
Possibly the worst ranking system I've seen is the World of Warcraft PVP ranking system. It basically rewards how often you play the game rather than the system which I'm use to in FPS - kills:death ratio.
The system has 14 ranks, which get progressively harder as you get higher up. The amount of damage you deal to a person decides how much 'honor' you get. Your honor is added up and your rank improves each week.
Now the problem with this is obviously the more you play, the more honor you get (much like XP).
In order to overtake ranks above you and achieve the top rank, you have to compete with their honor. With people playing all day everyday this is virtually unachievable to anyone but students or the unemployed.
Why reach the top rank? Well the rewards (weapons,armour) are within the top 3 in the game. This is the only reason I play (I don't have time to dedicate 5 hours a night to go to Molten Core or Black Wing Lair - and besides being a Paladin means I never get the decent sword as it will always go to a Warrior or Rogue. I get stuck with 'epic' armour that is meant for player-versus-environment healing).
I'm hoping they make the system a lot more intelligent in the future. Not kill:death ratio based, but make the objectives give much greater honor rewards, reward teamplay: e.g. healing,traps,saps and also honor-per-time-played used instead of the stupid grind crap at the moment.
Nothing costs nothing