A TL:DR of the new Performance Based Matchmaking & some PSAs for the season #RT

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The new Performance Based Matchmaking (PBM) has now hit the live server and since it became obvious that a lot of people still have some questions I wanted to post a final Twitlonger to explain a few remaining misunderstandings and also to make some PSAs that are directly related to it.

First you have to understand that rank and MMR are not the same. Your MMR is hidden, it is a number that reflects your skill level. Your rank is supposed to express that but it moves faster after wins and losses. After a game you now receive Personal Rank Adjustments (PRA) and the new Performance Adjustment (PA). The PRA is supposed to help your rank match your MMR faster. Assuming for example you are a player on GM MMR and you just completed your placements you'd be placed into Master 1000. You will now likely receive high positive PRA points because the system wants to increase your rank faster so it matches your high MMR. The new PBM system has also a small impact on that number but we will neglect that for the rest of this post for simplicity reasons.

Our main concern is the new Performance Adjustment System. After a match Blizzard looks at your performance on the hero you played in the last game and now cross compares how well you performed on that hero compared to the average performance of other players on your skill level on the same hero.
To make sure it's a fair comparison the system takes also into consideration the map, game length, region, skill level and if the game resulted in a win or loss. The algorithm that determines your performance uses 20 different factors, among them siege damage, hero damage, KDA, EXP soakes, CC time but also many others that are not publicly known. At the end of the process you receive a number between 0 and 1 that rates your performance, 0.5 representing a completely average game that would result in 0 PA points. Depending on what that number is you will now gain or lose a maximum +/- 50 PA points based on your performance.

IMPORTANT: you can only gain MMR points if you've won the match. The PA simply determines if you gain more or less PA points. If your team won the game, but you performed poorly you would receive negative PA points, but you would still gain MMR (just not as much as in the old system). If on the other hand your team lost the game, but you performed very well you would receive a positive PA, but you would still lose MMR overal (but not as much as you would have in the old system). Therefore winning or losing a game is still the most important factor of the system.

You are only compared to players of your own level. After a new hero is added or a patch changes a hero the game uses the old system (no PA) until a certain threshold of data is accumulated that's used as the baseline average on your level. Depending on hero, region and skill level this can take between a few hours and several days (example: Valla in EU in Gold/Plat vs. Cho'Gall in SEA in GM).

Strictly speaking the Match Creator and the Performance Based Matchmaking are different systems. The PBM kicks in AFTER you finished your game and now attempts to make sure you reach your actual MMR faster. This now affects the creation of the next match, so the PBM system is trying to provide the Match Creator with more accurate data to work with. That also means that it will take some time until we will see improvements on the quality of matches (not your rank!). Especially since you have to keep in mind that even if you play 30 games a day it does not mean the other 9 players in your game did as well. You might have played 200 games after the first week but some of the players you are matched with are only on their 10th game in the new patch. So while we can directly see the result of the PBM expressed as the PA Points after a game, we still have to be patient before we can expect an actual impact of the system on the mach quality itself (probably several weeks at least).

I hope this post could clear a few things up and explained the difference between your Rank and MMR. Finally I'd like to quickly point out that this system has nothing to do with the MVP system, which tries to determine the best out of 10 players in a single game instead of what the PBM attempts to do. The system is also not the same system that was used for Overwatch (which also allows for in-game hero swaps, which is a complete game changer for obvious reasons).
If you have additional questions I would highly recommend to watch this interview with the Heroes of the Storm Lead Designer about the PBM system: https://youtu.be/42bLcSb8jbI

Thanks for reading
- Khaldor

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