I was bored this offseason so I put together a spreadsheet based on the glicko 2 algorithm to see how the system works. There had been a lot of questions about how the initial placement matches work, and I thought the following plot was useful for showing how the system works.
The glicko 2 system has two parts to it, a rating and a deviation. The rating is your “skill level” and the deviation is a measure of how well the system thinks it knows your rating. The system is 95% confident your “skill level” is +/- two deviations from your rating. The guild wars 2 system will start you with a rating of 1200 and a deviation of 350. So it is saying it is 95% sure you will be somewhere between a 500 and 1900 rating. As you play more matches your deviation will go down to a point.
The example plot shows two players who both went 6-4 over their first 10 placement matches. The blue player ended up in high tier gold while the red player ended up in mid tier silver. The dots represent their rating, and the error bars represent the 95% confidence interval of that rating. Each player played matches against opponents that were within 150 rating points. The blue player won their first 3 matches while the red player lost its first 2. The first matches have the biggest impact on your rating. Also, there is still overlap between the players predicted skill level even with a ~400 rating difference since they have not played enough matches to have a very accurate rating.
One other thing to add. Season 5 started with a “soft reset”. Player’s rating was averaged with the starting rating of 1200. So people with a rating equivalent to silver started between 1125 and 1275, gold 1275 and 1325, platinum 1325 and 1575.
References:
http://www.glicko.net/glicko/glicko2.pdf
https://wiki.guildwars2.com/wiki/PvP_Matchmaking_Algorithm as of 2/15/16
