MATCHMAKING
Placement
Before being seated in a league, players must play a number of placement
matches. Battle.net uses these placement matches to estimate your skill
level and give you a starter point. The number of placement matches is
set to 5. This means that although the system will seat you in a league more
quickly, it may do so less accurately. Being placed in a league doesn't
cement you within that league, and if you are able to prove that you can
hang with players more skilled than Battle.net initially estimated, the
system will promote you to a higher league. Conversely, the system will
relegate you to a lower-level league if the opponents you are initially
grouped with prove to be too difficult. It is not possible to be placed
into the highest league, only promoted into the highest league.
Matchmaking Ratings
The prevailing theory behind the matchmaking system is that each player
is assigned a hidden "matchmaking rating", or MMR. MMR determines who your
opponents are, as well as whether you are promoted or demoted. When you
win or lose a game, your actual rating is compared with the MMR of your
opponent and points are awarded or deducted as necessary. MMR is only affected by
the end result of a match, not the means used to achieve those results.
In-game details such as APM, unit composition, and tech path of either player are
irrelevant.
An important reference point for understanding this theory is the WoW
Arena Matchmaking System<
http://forums.worldofwarcraft.com/th...Id=14910422788
<http://forums.worldofwarcraft.com/thread.html?topicId=14910422788&sid=1>
&sid=1>.
Examples
As Battle.net most closely resembles the WoW Arena system, we'll use
those values as a baseline. Remember that you cannot see your matchmaking
rating in SC2, but you can in WoW Arena. This becomes easier to estimate when
using WoW Arena as a reference because your MMR is what your team's rating is
expected to become if you continue playing at your current level, and
there are no hard separations between players.
It's generally accepted that the hierarchy of WoW Arena participants looks like this:
0-1499: Newbie
1500-1799: Average
1800-1999: Fairly skilled
2000-2199: Very skilled
2200-3000: Extremely skilled
If we expand that to SC2, we would get Bronze, Silver, Gold, Platinum,
and Diamond, respectively.
In WoW Arena, your MMR - which is persistent across arena seasons -
starts at an average level while your team rating starts at 0. If you go 10-0
for your first 10 games, your MMR would probably skyrocket to 2200. The
reason for this is that the system is unable to accurately determine your skill
level, so your MMR rises more rapidly (called "volatility") in the hopes
that it finds an upper bound. Even though your team rating will only be
about 460 after going 10-0, you at that point would be playing against
the most skilled players because your MMR is so high. The longer your win
streak, the more your MMR increases until you are playing people that
cause you to win 50% of the time. Once you start losing more games than you're
winning at a certain level, your MMR starts falling until it can
comfortably seat you. As you get closer to a 50% win rate, your volatility drops and
therefore your MMR doesn't rise and fall as dramatically as it did at
first.
The system acknowledges that just because your MMR is a certain level,
you may not always perform at that level. There is some allowance involved.
Search Functionality
The Battle.net matchmaking system will find opponents that are close to
your skill level. The degree of accuracy had yet to be determined by Rob Pardo
according to this interview<http://www.escapistmagazine.com/news/view/99211-Battle-net-StarCraft-II-Matchmaking-Too-Good>.
You will notice after a short time that the message "EXPANDING SEARCH..."
will appear when searching for a game. This means the system is searching
for opponents that may be higher or lower than your intended level.
What is not clear is whether the system eventually and continually
expands the search until any opponent is found, or whether it merely widens the
allowable MMR variance.
LEAGUES
League Overview
Leagues are divided by MMR breakpoints and not percentiles. However, due
to the nature of MMR breakpoints, there are general trends that emerge, such
as a bell curve for each region. Thanks to sites like
http://sc2ranks.com/stats/ we can see proof of this. For example, in
Korea, at the time of this edit (8/7), 29% of players were in Bronze while in
Southeast Asia, 37% of players were in Bronze. Note that currently it is
not possible to be placed directly into Diamond league, and that players can
only be promoted into Diamond league.
Promotion and Demotion
In order to be promoted to a higher league, your MMR must sit comfortably
within the boundaries of that league, meaning you'll need to be averaging
a 50% win rate against those kinds of players. If you are a 2250 MMR
Platinum player who typically faces Diamond players, you will need to not only
average a 50% win rate against those Diamond players, but also maintain a
much higher win rate against any Platinum players you may encounter. Once
your MMR reaches a certain threshold you may be eligible for promotion.
The system periodically re-evaluates your placement every X games. X
varies and nobody knows because Blizzard is explicitly not telling us, however
according to a recent interview with Dustin Browder, your initial
promotion or demotion will be evaluated after about 30 games. These are called
"review checkpoints" and it is important to remember that the result of the
promotion or demotion reflects your persistent MMR relative to the
required MMR breakpoints, and may not be consistent with the result of your most
recent game. If your eligibility for promotion remains unchanged at the
time of checkpoint, you will be promoted.
For example, if the Diamond MMR breakpoint is 2200 and your MMR is 2250
at the time you hit a review checkpoint, you would be promoted.
Dropping down to a lower league works the same way, only by losing.
You do not need to reach #1 (or any particular rank) in your division to
get promoted.
Divisions
Leagues comprise a number of divisions that are all ranked equally.
Divisions cap out at 100 players. As a division gets closer to 100
players, a new division may be created with new players evenly distributed across
each division until some eventually start capping out.
RATING
The important thing to know is that rating only determines your standing
within your own division. And even then, only indirectly, because you are
playing against opponents beyond your division's player pool.
Team Ratings
Your team wins or loses as a whole. If your partners left the game early
and you stuck around to defeat your opponents, your entire team will be
credited with a win.
"Rating Inflation" and the Bonus Pool
The Bonus Pool is a pool of points that are awarded whenever players are
placed into a new League. The Bonus Pool also accrues over time. Whenever
a game is won, an amount equal to the rating earned is deducted from the
Bonus Pool and added to the player's rating.
This has the effect of increasing player ratings over time. On the
surface, this appears to be a negative thing. However, War3's Ladder system had XP
decay beyond a certain level. Rather than forcing players to play games
in the fashion War3 used, SC2 encourages players to play by generating a
Bonus Pool.
The Bonus Pool accrues at a rate of 1 point per 2 hours, whether the
player or team is active or not. The Bonus Pool also begins building based on
when the ladder season began. That is, if Player A was placed into a division
and started with a Bonus Pool of 100, then 24 hours later Player B placed
into a new division, Player B's Bonus Pool would be 112.
Originally Posted by hideinlight
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