This seems to be a common issue that people seem to be having, and I’m seeing a good number of posts along the lines of:
“I won 2 matches 500:400 and 500:300, yet match A was only +X MMR, and match B was +Y MMR” where X or Y is higher than the other. Actual numbers don’t really matter.
By my understanding, how much MMR you gain or lose depends on your MMR, your team’s average MMR (possibly), and the opposing team’s average MMR.
Examples (I think this is how it works, relatively):
Your own MMR is 1350 for all of the following scenarios:
1) Opposing team’s MMR is 1400, and your team wins. You gain, let’s say, 30 MMR.
2) Opposing team’s MMR is 1500, and your team wins. You gain, 50 MMR.
Why is scenario 2 higher? Well, the opposing team’s MMR is much higher than your own, and presumably, your team’s MMR. The odds of actually winning that match is low, but you won it anyway. You should be rewarded more for it.
3) Opposing team’s MMR is 1300, and your team wins. You gain, let’s say, 15 MMR.
4) Opposing team’s MMR is 1200, and your team wins. You gain, 10 MMR.
Explanation: If the opposing team’s MMR is much lower than your own, the odds of you winning is higher. It’s basically a stomp. Should you be rewarded more for stomping the team when it’s an obvious win?
Let’s look at some losing scenarios:
5) Opposing team’s MMR is 1400, and your team loses. You lose, let’s say, 30 MMR.
6) Opposing team’s MMR is 1500, and your team loses. You lose 10 MMR.
If you lose to a team that’s significantly higher than your own MMR, which is expected by match prediction, your penalty should not be as high as if you lose to a team that’s closer to your MMR.
7) Opposing team’s MMR is 1300, and your team loses. You lose, let’s say, 30 MMR.
8) Opposing team’s MMR is 1200, and your team loses. You lose 50 MMR.
For scenario 8, the reason you lost more MMR was because the opposing team’s MMR was significantly lower than your own. Matchmaking predicted that you’ll win the match, but your team didn’t, so you’re penalized quite heavily for it. If you lose to a team that’s only slightly lower MMR, your MMR loss shouldn’t be too high.
These are all hypothetical numbers. We don’t exactly know the details of how MMR changes are calculated, as Glicko2 has multiple steps to determine that (excluding modifications made for 5v5 matches).
Since skill rating is now visible, two things would be nice to have:
1) MMR changes shown in match history. Evan already mentioned that this should be doable now that skill rating is visible. Perhaps even include things like your team’s average MMR vs. the opposing team’s average MMR (without revealing MMR of individual players in both teams, although it’s easy to add players on the opposing team and see their MMR).
2) Some details on how the MMR changes are calculated, to give a rough idea, particularly, what factors affect the change in MMR.
Note: Team score probably doesn’t play a direct role in calculating MMR changes, but it does give some indication of your MMR relative to the opposing team’s MMR. Example: if your MMR is 1200, and you win 500:400 against one team, and 500:300 against another, you can infer that the opposing team’s average MMR was around 1100 in the first match, while the second match’s opposing team may have been 1000 average MMR. (Again, hypothetical numbers).
