What is TrueSkill?
Microsoft Research:
The
TrueSkill™ ranking system is a skill based ranking system for
Xbox Live developed at
Microsoft Research. The purpose of a ranking system is to both identify and track the skills of gamers in a game (mode) in order to be able to match them into competitive matches. The
TrueSkill™ ranking system only uses the final standings of all teams in a game in order to update the skill estimates (ranks) of all gamers playing in this game. Ranking systems have been proposed for many sports but possibly the most prominent ranking system in use today is
ELO.
TrueSkill is simply another way, a different formula (quite literally) for finding out where you rank is in a particular online game. When you go to play a game, you have your average score - how well you have done overall in your past games.
TrueSkill takes it to another level by adding another variable - a degree of uncertainty in your skill. Since your average score doesn't tell you anything about your actual skill. You could have won every game you've ever played, though only playing with rookies, or you could have won every game by playing with the veterans and highly skilled players. Obviously winning against other skilled gamers should have more weight towards your ranking than playing against rookies. The uncertainty level is just that - its a range of where you might actually be in your skill. If you've only played a few games online with Project Gotham Racing 3 for example, your uncertaintly level is large because TrueSkill doesn't know where your actual skill lies. As you play more games, your average is calculated, and the level of uncertainty is reduced because the system is able to pinpoint how you do against the other ranked players -- rookies, novices, contenders, professionals, hotshots, and so on. The TrueSkill
ranking system maintains a belief in your skill and assumes that your performance in a particular game varies around your skill.
This all probably seems very confusing, especially when you look at a nice algorithm like this one:
μwinner ← μwinner + σ2winner/c * v((μwinner-μloser)/c,ε/c)
μloser ← μloser - σ2loser/c * v((μwinner-μloser)/c,ε/c)
σ2winner ← σ2winner*[1-σ2winner/c2 * w((μwinner-μloser)/c,ε/c)]
σ2loser ← σ2loser*[1-σ2loser/c2 * w((μwinner-μloser)/c,ε/c)]
c2 = 2β2 + σ2winner + σ2loser
But don't worry, its all good stuff. Like I mentioned earlier, it is a worthy method to finding your true gaming skills.
Furthermore, the system works like your morning schedule. If you continue to do the same thing every day, your routine is concrete, and the outcome is usually the same (leaving for work around the same time each day, etc.). Like games, if you were matched with the same people for 3 of the same games, your outcome should be the same for all three - either coming in first or last, or somewhere in the middle. TrueSkill would notice that you do the same, and your certainty level would remain the same, and your level unchanged. But, say instead of taking a shower first thing in the morning, you eat breakfast and brush your teeth. You surprised your own system (alright, now I realize this wasn't the best example, but lets continue)! You might have finally figured out that if you take your shower too early your hair is too dry after you eat breakfast, and it is why you've been having problems styling it. This shows that you gained experience, and were able to change. Again, similarly, if you learned by watching your opponents in the first round of that one game, on the second round you should do much better to signify you know whats going on, and you've learned from playing those people several times. TrueSkill is able to see this, and will probably have you gain rank. Or, alternatively if you lose after winning many rounds, you will definately lose rank because for some reason you didn't do so well against your opponents.
There are many other possibilities of the TrueSkill ranking system such as in team games, individual games (1v1 x7 others for instance), and objective games. Each is based upon averages, and whether you win or lose. Obviously winning games will only help, and losing won't do anything for you, its pretty simple looking at it this way. However, averages isn't the only thing to your skill, its how well you might do, and how well you actually perform.
Heres another example of how the system works. Say you are literally the worst gamer in the world (though we know you arent). You've played so many games, but you lose them all no matter how hard you try (and no, this isn't a personal reflection, mind you). Instead of continuously losing, you decide to take time off from ranked games, and practice in training or unranked games. You practice so hard, that you return to become the best player in the world. You play your first ranked game, and its a total pwning at heart, you have no mercy. The TrueSkill system will see this, however because the system had the belief that you would lose you won't really gain too much. You would have to win many more games (anywhere from 50 to 100 games) before the system can really notice your major change and your rank moves to the "uber-skilled" side. Remember, the system is based on the belief, or projected outcome of your games. If you always lose, the system will say "hey, you always lose, what says you won't lose this time?" As you get better, and win some games the system might say "hey, you won this game, but you still lost every game before." So, it will take some time for the system to notice any real huge change.
This graph is basically what the TrueSkill system is. The average skill of the gamer represents
μ, while
σ represents the level of uncertainty in the gamer's skill. I know, a bit confusing. Who knew your skill could make a graph like this one?
So, it is safe to say that the TrueSkill ranking system really does give you your true skills, with no questions asked. It is nearly flawless although factors such as having cheaters and quitters on your team or as your opponents will mess up the system occasionally. If you are really curious about this system you can check out the official TrueSkill page at
Microsoft Research, but be warned it is pretty brain-intensive!
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