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THE STARCRAFT BATTLE.NET LADDER RATING SUMMARY FAQ

(Taken from http://www.battle.net/faqs/starcraft/ladder.htm)


----- OVERVIEW -------------------------------------------------------------------
   
Battle.net maintains both a win/loss record and a rating for each player who 
plays in ladder games. Players gain rating points for each win, and lose rating 
points for each loss. Because ratings take into account not only the number of 
wins and losses but also the skill of each opponent, they are a useful measure of 
the true skill level of a player.  

The rating system used by Battle.net is the same Elo rating system that used in 
competitive chess, golf, and tennis. The Elo rating is a scientific model which 
provides a meaningful way to compare the skill level of different players, based 
on the assumption that skill levels follow a normal bell curve.  

This FAQ provides an overview of how the rating system works, and how Battle.net 
maintains its ladders.

----- LADDER GAMES ---------------------------------------------------------------

Only ladder games count towards your rating and ladder standing. To create or 
join a ladder game, select the "Ladder Game" option from the list of game types. 
You must accumulate at least ten non-ladder wins to be eligible to create or join 
ladder games.  

Ladder games do not allow teams, allies, or shared vision. Ladder games also have 
the game speed fixed at the "fast" setting.  

Ladder games which last less than five minutes are not counted towards your 
record, rating, or rank.

----- PROBABILITY OF WINNING ----------------------------------------------------

Battle.net computes the probability of each player winning a ladder game based on 
that player's rating and the ratings of each of the players he is playing against.
This probability is used to determine how many rating points the player wins or 
loses for winning or losing the game. A player who wins against a much higher 
rated player will gain many points for the victory, while a player who wins 
against a much lower rated player will gain very few points.  

For two player games, the following formula is used to compute the probability of 
winning:

	Probability = 1 / (1 + 10(-difference_in_ratings / 400))

You can use the following charts to quickly estimate your probability of winning 
against another opponent:


      WHEN PLAYING HIGHER RANKED	      WHEN PLAYING LOWER RANKED
     Rating Dif.  Prob. of Winning	   Rating Dif.   Prob. of Winning 		
	400 		9.1% 			0 		50% 	
	350 		11.8% 			50 		57.1% 	
	300 		15.1% 			100 		64% 	
	250 		19.2% 			150 		70.3% 	
	200 		24% 			200 		76% 	
	150 		29.7% 			250 		80.8% 
	100 		36% 			300 		84.9% 
	50 		42% 			350 		88.2% 	
	0 		50% 			400 		90.9% 	

When more than two players participate in a ladder game, probabilities are 
adjusted downward accordingly. For example, in a three player game, each player's 
probability of winning is divided by 3/2.


----- DEVELOPMENT COEFFICIENT ----------------------------------------------------

Each player is assigned a development coefficient (K), which determines the 
maximum number of rating points that can be won or lost in any one game. The 
development coefficient starts at 25 and then drops lower as the player becomes 
more experienced. This enables new players to move quickly towards a rating that 
reflects their true ability level, while adding a level of stability to the 
ratings of more experienced players.  

The development coefficient is calculated according to the following rules:  

	K=25 for new players  
	K=15 for players who have played 30 or more ladder games  
	K=10 for players who have attained a rating of 2400 or higher 	
	     (even if their rating later dropped below 2400).

----- RATING CHANGE --------------------------------------------------------------

Each player who completes a ladder game wins or loses points according to the 
following formulas:  

	Winner's rating increases by K * (100% - probability_of_winning)  	
	Loser's rating decreases by K * probability_of_winning  

Players who are disconnected a ladder game prior to the completion of the game do 
not gain or lose any rating points. However, they gain one disconnect. Because it 
is possible that some players may intentionally disconnect their system from the 
Internet rather than take a loss, you should be wary of playing against any 
players who have a high number of disconnects.  

Battle.net does not award any rating changes for a ladder game unless there was 
at least one winner and at least one loser, and the game lasted at least five 
minutes. Also, if any winner gains one or more rating points, Battle.net ensures 
that each loser loses at least one rating point, even if their probability of 
winning was so low that the computed rating adjustment rounds to down zero.  

----- LADDER ---------------------------------------------------------------------

The top 1000 rated players in the world are given official rankings on the 
Starcraft ladder. Ladder rankings are recomputed every night at midnight Pacific 
time.  

Ladder games which include one or more ranked player are automatically reported 
to the Ladder Games forum. In order to keep the volume of posts reasonable, 
ladder games which do not include any player in the top 1000 are not posted.  

Each ladder lasts for three months. At the end of a three month season, Blizzard 
declares a world champion for that season, and resets the ladder and all ratings. 
The world champion is the person who was ranked #1 at midnight on the last day of 
the season. The seasons are as follows:  

	Winter Ladder Dec 1 - Feb 28/29  
	Spring Ladder Mar 1 - May 31  
	Summer Ladder Jun 1 - Aug 31  
	Fall Ladder Sep 1 - Nov 30.

----- REPORTING ABUSES -----------------------------------------------------------

It is considered an abuse of the ladder system to:  

	Repeadly play the same opponent(s),  
	Intentionally lose to an opponent to increase his rating, or  	
	Disconnect from a game for the purpose of avoiding a loss.  

Because the results of all ladder games between ranked players are posted to the 
Ladder Games forum, any interested observer can easily check the record of a 
ranked player to see if he is repeatedly playing against the same opponents or 
repeatedly disconnecting from games.  

Please report all suspected abuses of the ladder to "support@blizzard.com". 
Include as much information as possible documenting the pattern of abuse. 
Blizzard may, at our sole discretion, delete the Battle.net account of any player 
suspected of abusing or attempting to abuse the ladder system.

