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StarCraft II Ladder Update -- April 27, 2015

StarCraft II Ladder Update -- April 27, 2015

With the new ladder season upon us, many players have already noticed the effects of some new changes that we’ve implemented. With some adjustments previously made in Season 1, the new season provided an opportunity to implement a larger set of changes that would be risky or impossible to implement mid-season. We’d like to review the changes and how they will affect the matchmaking and ranking system.

Issues in the New Season
Before we go over the changes, a few issues have popped up in the new season and caused some confusion. We’d like to address those issues to help provide some clarity.

MMR Adjustments
Contrary to claims from some in the community, player ratings in Season 2 haven’t been reset. Instead, player ratings have been adjusted proportionally and ladder placement matches have been reset to help give players a placement that more closely reflects their actual overall rating.

However, a reason that many players believed player ratings were reset was due to an unintended side effect. The clearing of placement games unintentionally triggered an additional piece of ladder promotion logic normally intended for new players.

The “New Player” Logic
When a new player plays their first matches, the system assesses their performance in order to determine their MMR rating. The system also pairs this rating with another piece of logic called “uncertainty”. Uncertainty represents how confident the system is in your current rating. MMR and uncertainty are updated after every match and the system progressively attempts to predict your skill in relation to other players.

Early in development, some players were having too much trouble progressing through leagues. With a high level of uncertainty in their MMR, there was the potential for them to be placed in a league that exceeded their actual skill level.  Due to this, the “new player” logic was built into the system to help ensure that newer players were more conservatively placed. This offers a better sense of progression as new players are given an opportunity to be promoted into new leagues once the system is more confident in their actual skill level.

In the current system, it takes around 25 games to pass the “new player” game boundary. This is the point in which the player’s uncertainty level has decreased to a point that the system is confident it has an accurate assessment of the player’s skill level.

While this logic has affected players’ initial league placement in the new season, we believe that all our active players will quickly get into the league they deserve. We apologize to any players who worked hard to achieve their rank and felt that we stripped it from them.

Problems During the Season Roll
The season roll timing has also led to some confusion. Things didn't quite go as planned, and while we have a high level of confidence in the math we applied to adjust ratings, we ran into a few implementation issues very close to the season boundary. We extended the season roll to provide more time to sort out these issues, but it wasn’t correctly scheduled in all regions. CN, KR/TW, and SEA rolled into Season 2 before we could deploy our MMR adjustments. While it wasn’t our intention to have different MMR adjustments in different regions, it does give us a chance to measure how the changes perform against a baseline and then respond to concerns from players in the next season.

Changes for This Season
Now we’d like to outline some of the changes we made for Season 2. While we touched upon some of these in our previous ladder update, we have a few additional changes to review.

Removed “MMR Decay”
“MMR decay” attempted to simulate the skill loss that would occur for an inactive player by lowering their MMR after a certain period of inactivity. While this functioned as expected for a period of time, eventually activity patterns from some players caused this functionality to have undesired effects. Now that it has been removed, inactive players will no longer see their MMR rating affected.

Proportionally Adjusted Player Ratings
Since we were unable to trace the effects of “MMR decay” on all player accounts, we have applied a proportional adjustment to accounts that we could positively identify as being decayed. Players in Diamond and above should retain their overall position and should be promoted into their proper league soon. For everyone who has been adjusted, the system has been tuned to more quickly adjust to changes in player skill. If you feel your rank is too low, please give the system 10-30 games to catch up to your current skill level. Unfortunately, the effects of “MMR Decay” for players who were only partially active in previous seasons have also caused a shift in higher players ratings that is only now being felt. Players in the Gold to Diamond league range should find their rating adjusted quicker to start the season. Players in Masters and above should still retain their overall rating but may need to break through the “low ball” barrier.

Removed League Threshold Checks
Previously, checks were in place requiring players to progress past the league threshold by a certain win percentage before a promotion. This was so players near this threshold would not ”rubber-band” back and forth between higher and lower leagues as they won and lost matches. This logic is no longer necessary given that mid-season demotions were removed some time ago. Players will now be promoted the moment their MMR meets the requirement of the new league.

Players on Win Streaks Can Now be Promoted
Previously, when a player went on a winning streak the system became less certain it was accurately assessing the skill level of the player. Thus, a league promotion would not occur until the player lost and the system was more certain of where the player should be placed. This behavior has been changed so that players on win streaks will be promoted as soon as they’re eligible.

Tightened the Rating Range When Finding a Match
When looking to find a match for a player in matchmaking, the system would previously look for opponents within a certain rating range. We’ve adjusted this behavior in the new season and tightened the rating range. This should allow for more consistent matching between players of similar skill level.

Re-adjusted League Distribution Percentages and Starting MMR for New Players
We’ve also re-adjusted the league distribution percentages and the starting MMR for new players to compensate for all the changes above.

Thanks to everyone who has offered feedback on their ladder experience. We’ll continue to monitor how these changes are working out and consider additional improvements that can be made in the future.

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