Hoo boy....

Guild Wars 2

Matchmaking
Primary article: PvP Matchmaking Algorithm
The PvP matchmaking algorithm is the Glicko2 matchmaking rating (MMR) and helps match players with other players with similar skill levels.
It is used to place players queueing for Ranked and Unranked arenas.
The metrics used during matchmaking include: rating, rank, party size, profession, ladder position, and dishonor.
Players can search for parties for Unranked and Ranked Arenas in categories in the Looking For Group tool.

Auto-Balance
Games will no longer autobalance after one team has reached 80% of the maximum score if the game ends by score.
Games will no longer autobalance when within two minutes of the end of the game if the game ends by time.
Autobalance functionality has been updated to give a new volunteer bonus to any players who volunteer for balancing, as well as giving any players balanced the winner bonus. When volunteers are lacking, random selection will be used.
Volunteer Rewards gives volunteers guaranteed win credit, even if they end the match on the losing team. Volunteers also receive a 25 rank points bonus. [verification requested]
Dishonor
Dishonor is a system to prevent players from joining unranked and ranked arenas after player misconduct, such as leaving or not participating (AFKing) in matches. Each instance of undesired behavior will immediately result in a timeout and increase the player's dishonor stat. Frequent misbehaving will result in increased duration of timeouts.

The dishonor system also includes a protection system and entitles the match in the players history accordingly, if one of the parameters applied.

Parameters
Desertion - You disconnect the game: You will be punished by the dishonor system.

Byes - One or more players of the enemy team disconnect from the match: You will get less rewarded for winning.

Forfeits - One or more players from your team disconnect the match: You will get no punishment.

Win/Lose ratio
Taking above parameters in consideration, a players W/L ratio can be calculated with the following formula:

totalGames = wins + losses + desertions + byes //forfeits do not count as win or lose, making it invalid for the formula.
winRatio = ((wins + byes)/totalGames)*100 //win ratio in %
lossRatio = ((losses + desertions)/totalGames)*100 //lose ratio in %
wlRatio = winRatio/lossRatio //W/L ratio as a float.