Matchmaking

The system guesses how good you are based on who you beat and who you lose to. It tries to make matches where it thinks you have a 50/50 chance of winning.

It knows pre-made teams are an advantage, so it gives you tougher opponents when you are in a pre-made team. We did fancy math to make the pre-made teams vs solo players matching fair. I even ran it by two math Ph.Ds and they said it made sense!

Details
The basic concept is that the system over time understands how strong of a player you are, and attempts to place you in games with people of the same strength. As much as possible, the game tries to create matches that are a coin flip between players who are about the same skill.

The basic priorities of the system are in order: 1) Protecting newbies from experienced players. 2) Fairness & creating competitive matches 3) Finding a match at all. The longer you wait, the less important priorities #1 and #2 are.

How are matches made?
Step 1: Determine your strength:

* If you solo queued, it’s just your personal rating (i.e. ranked team rating for ranked team, normal games rating for normal games). * If you are in a pre-made team, your rating is the average of you and your team members, along with an increase based on the type of pre-made you are to make sure that you get tougher opponents, because being a pre-made is an advantage. This bonus is calculated from a bunch of research we did on hundreds of thousands of game results to figure out how much of an advantage being in a team is. We do some behind the scenes adjustments as well for stuff like beginners paired with pros, etc.

Step 2: Determine who your eligible opponents might be:

* Initially, the system will only match you with very similar players based on the rating you have been assigned. Eventually, it gives you less ideal matches because it doesn't want you to be in line forever. * Newbies get some special protection and are usually matched vs other newbies.

Step 3: Find a match:

* Eventually, the system finds a match that is fair for everyone involved, and puts the players into a game. * The system then tries to balance the team to make two teams with 50% odds of winning. In our mid-beta pool, which has very few players relative to what is in release, the majority of games created by the system had teams predicted to be extremely fair (no team with odds greater than 55% to win). We expect that in release, that 98%+ of the time we will see games where no team is thought by the system to have a higher than 55% chance to win. This is because adding a small amount of players to the system dramatically improves the quality of matches made, and we expect a lot more people to be playing at release than in closed beta.

How is my rating measured over time?
We use a modified version of the Elo system. The basic gist of the Elo system is that it uses math to compare two player ratings to guess the game result – like, “Bob will win vs Jim 75% of the time”.

From there, the game is played. If you win, you gain points, if you lose, you lose points. If your win was “surprising” (i.e. the system thought you would lose), the points you gain are larger. Additionally, if you are a newer player, you gain and lose points more rapidly so that you get to your skill level faster. Over time, this means that good players end up high rated because they do better than the system expects, until the system is guessing correctly how often they will win.

We modified this for team use, and basically, the concept is that you get a team elo based on whoever is on the team, and if you win, it’s assumed that everyone on the team was “better” than the guess, and gains points. There are some problems with this, but it generally works out, especially if people use pre-mades a little bit.

We also do a few little things to nudge your elo rating in the right direction when you start out so that people get where they need to get faster.

* We use various proprietary methods to identify players that are significantly more skilled than a typical newb, and boot their rating up a bunch behind the scenes when we notice this. * Gaining levels boosts your elo rating a lot. This further helps separate level 30 summoners from low level summoners.

For more details on how the Elo system works on a theoretical level, you can read about it at: http://en.wikipedia.org/wiki/Elo_rating_system

So wait, how did you determine how to deal with pre-made teams vs solos? Some matchmaking pools avoid this completely by only allowing 5 man pre-mades vs 5 man pre-mades (ranked games, etc).

Others mix pre-mades and solos freely, and to be fair in these cases, we performed analysis on several hundreds of thousands of games to identify how much of a skill advantage this gives people. We found that a variety of factors influence how much of an advantage being a pre-made is, ranging from the size of the pre-made (i.e. 2,3,4,5 people), to the skills of the players involved, to combinations of pros and newbs, to other more subtle factors that must be used as well.

Having found these advantages, we know how much we need to boost your rating by in a team to make a fair match, and apply the appropriate, mathematically justified adjustment. These results in some cases are very surprising (while still appearing correct in the statistics)

While we will not give precise values because those are trade secrets, we can say that: 5-man pre-mades are only moderately stronger than solo queuers. Partial pre-mades are only a little bit of an advantage. Newbs don’t benefit much from being in a pre-made, while experts benefit a lot.

Okay, fine, but why do you even match pre-mades vs non-premades at all? There are a few reasons for this:

* It helps the system find your skill rating much faster, so that you get fair matches faster. This works because if you pre-make, it reduces the amount that “bad” or “good” luck related to your teammates causes you to win or lose games. If you pre-make, you join up with people of about your skill, and you now get less random teammates boosting you/screwing you, so your rating gets to an accurate value more quickly because more of each game result is due to you and your friend, who are close in skill. * We want people to easily play with their friends because they will have more fun if they do, and you can’t have a 5v5 matchmaking pool of all 2 man teams, or all 3 man teams – you need a mixture for it to work. We chose to include 5-man because it’s a lot of fun – if we have large enough pools later, we might separate 5-man premades from the partial pre-mades – but the data we have shows that this won’t improve the fairness of matches much at all, it will be about the same.