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United States11874 Posts
Based on mounting evidence and independent research, MMR does appear to decay over periods of inactivity. Korona from MMR-Stats first noticed this when it appeared the league offsets from the previous season did not change, but the reported point changes (and therefore inferred MMR values) indicated a dramatic drop in opponent quality for users who had long stretches of inactivity. You can see an album of three examples posted by Korona to illustrate this:
http://imgur.com/a/vaLDF#0
Why Does MMR Decay Exist?
As some might recall, many players actually requested that some sort of decay mechanism be implemented because they didn't feel they could compete at their normal level after returning from a long break. For example:
http://eu.battle.net/sc2/en/forum/topic/2868804407
http://us.battle.net/sc2/en/forum/topic/7179568535
Blizzard apparently agreed, and now MMR will decay if users have not played games for a certain period of time.
How Much Does MMR Decay Due to Inactivity?
Korona is still looking through MMR-Stats records, but there seems to be an upper limit of about 310 or so rating which is a little larger than the span of most leagues. If you're very inactive, you could drop one league (or, if you're already near the bottom of one league, up to two leagues) upon returning. Note that if you are inactive in a season and return in the same season, you will remain in the same league because you can no longer be demoted mid-season, but you will face lower-league opponents because MMR transcends league boundaries. This means that if you have experienced MMR decay mid-season, your league icon no longer reflects your current skill level.
Note that so far, we have not discovered any examples of players dropping more than the 310-ish value. However, we do not believe that this value applies evenly to inactive players, meaning the amount of decay is probably gradual beginning at some point and increasing up to this limit.
Also note that the existing MMR lookup rule applies: if you are inactive for an entire season (that is, you stop playing in Season n, you play no games--ranked or unranked--during Season n+1, you come back for Season n+2), your MMR is wiped clean.
What Impact Does MMR Decay Have on the Overall Ladder?
On an individual basis, decay is a fine concept. You come back from a break, you're a little rusty, so it's fair to match you against people who are a little weaker. On a macro scale, it depends on the overall activity level of the ladder.
I hope to update this post soon with inactivity filters included, if I can get a handle on them.
How Frequently Must I Keep Playing to Prevent Decay?
Decay begins to take effect between 2 weeks and 4 weeks of uninterrupted inactivity. We believe the effect to be linear, from a decay of 0 at 2 weeks to about 310 at 4 weeks. The below image illustrates.
![[image loading]](http://i.imgur.com/8TT5AnH.png)
The red line is the decay rate. x is time in days and y is decay amount. The decay hard caps at the blue and green lines.
Does MMR Decay Result in Ladder Deflation?
Based on the current activity levels of the ladder as a whole, it appears that MMR decay does have a deflationary effect. As noted, if over half the Platinum players go inactive and get decayed down to Gold, as long as their skills deteriorated at similar rates, they would be evenly matched against each other which means their ratings would not increase. However, against legitimately weaker true-Gold players, they would still win, which would effectively push the Gold players further down. As long as the inactive members constitute a majority of the player base, system-wide deflation is inevitable.
Is MMR Decay Overtuned?
It is arguable that the current upper limit of MMR decay is too aggressive. It's jarring for players to suddenly find that they are starting a new season in a lower league despite feeling that they were competing effectively in their higher league, only because they didn't play enough games. On average, players earn 16 MMR for a win against an opponent of equal strength. A decay-driven rating drop of 300 means that it would take nearly 20 wins over losses to return to a player's previous strength. Assuming you never lost, it would take you 20 games to overcome. However, according to my research, only 5,928, or 17.02%, of Bronze players played more than 20 games in Season 4, compared to 37.83% of Silver, 58.20% of Gold, 69.20% of Platinum, 77.59% of Diamond, and 85.70% of Master players. Overall, 52.12% of players will not play enough games to offset the maximum amount of MMR decay over the course of a season.
Notes
Decay triggers only after an uninterrupted inactivity period . Korona should have better visibility on this as time passes, but it shouldn't affect the integrity of the majority of information presented here.
+ Show Spoiler +Incorrect/Legacy Information The data captured reflects the Americas server. For Bronze league, 3,261 of 34,812 players (9.3%) had bonus pools below 1 week's worth by the end of last season. 3,691 (10.6%) had bonus pools below 2 weeks' worth. 4,165 (11.9%) had bonus pools below 3 weeks' worth. 4,718 (13.5%) had bonus pools below 4 weeks' worth. 5,598 (16%) had bonus pools below 5 weeks' worth. 7,775 (22.3%) had bonus pools below 6 weeks' worth. For Silver it breaks down like this: <1 week's worth of bonus pool by season end: 11.91% <2 weeks: 14.9% <3 weeks: 18.4% <4 weeks: 22.8% <5 weeks: 29.1% <6 weeks: 40% of the Silver population Here's the full breakdown if you're curious: ![[image loading]](http://i.imgur.com/igMs9eR.png) Now, 6 weeks is pretty generous when you're talking about someone being an active player, so it's a pretty safe bet that the actual activity metric is below this. The fact that only 22% of Bronze players meet this criteria means that if you're playing at a Bronze level, 22% of the time your random opponent may be actual Bronze-level, while 60% or more of the time it may be an inactive Silver. It's more common for higher-level players to keep up in activity. On average, around half of the Master and Diamond populations kept their bonus pools low. However, that's still a 50-50 shot that you're playing someone who experienced MMR decay versus someone proven to be at that level.
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I believe this has always been the case right? Thank you for the research BTW.
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Awesome. So if I ever dare to play again after 2+ years I won't get my ass kicked by masters. I probably belong in silver now
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Brilliant post, and explains my own experience as a very infrequent player and the reported experience of many others. Unless you play a lot more than a casual player can, you end up being pushed down aggressively by MMR decay. But you're not the only one, resulting in playing much better players in lower leagues.
A further consequence, that you did not bring out, is that MMR decay randomizes your opponents. They could be much lower or much higher in actual skill, depending on their level of activity.
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On September 21 2013 07:05 Excalibur_Z wrote:However, according to my research, only 244, or 0.7%, of Bronze players played more than 20 games last season, compared to 1.5% of Silver, 2.2% of Gold, 2.7% of Platinum, 2.7% of Diamond, and 2.9% of Master players. Overall, 98% of players will not play enough games to offset the maximum amount of MMR decay over the course of a season.
Wow, and here I thought I play too few ladder games to call myself an active ladder player (<30 wins last season). :o
I guess that also explains why the gold players seem to have become better than compared to one or two seasons ago.
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On September 21 2013 07:23 FallDownMarigold wrote:
Awesome. So if I ever dare to play again after 2+ years I won't get my ass kicked by masters. I probably belong in silver now
MMR was already completely deleted in WoL if you skipped a whole season, had your lovely 5 placement matches against other beginners.
Had always some longer breaks from ladder and felt like I fought way weaker opponents when I played ladder again. Might have been some MMR shifts due to changing player numbers if there really was no decay before. Oh well will get an even more insane winrate if there is a real decay now ... and will have to play more ladder games to get good opponents again.
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4621 Posts
The most shocking part of this was the part with only around 3% of Master players play more then 20 games per season.
That is seriously quite low, I get more in just one day easily and I still feel casual.
Overall I think the MMR decay is a good feature, maybe not as extreme as the current model but some sort of decay is good.
And yes, this could explain some of the weirder games I've had this season, like hitting a plat player one game and then the very next game hitting a masters.
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On September 21 2013 07:46 Destructicon wrote:
The most shocking part of this was the part with only around 3% of Master players play more then 20 games per season.
That is seriously quite low, I get more in just one day easily and I still feel casual.
Overall I think the MMR decay is a good feature, maybe not as extreme as the current model but some sort of decay is good.
And yes, this could explain some of the weirder games I've had this season, like hitting a plat player one game and then the very next game hitting a masters.
At least now I have a reason to play Ranked games o_o;
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still need a reset mmr button.
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Assuming these metrics are true (98% of players don't play 20 1v1 games a season), then I'm happy the decay is that aggressive. Anyone playing that casually should move down the ladder, over time (a couple seasons) it will mean overall more accurate representation of your "skill" vs your displayed league. It will be hard to stay in diamond let alone masters, unless you know, you play frequently as I'm sure many of us do.
Then again, I don't think that number is too surprising, SC2 sold very very well, millions of copies, but the vast majority of those people aren't following esports and aren't about competitive 1v1 games, they enjoy all the other features of sc2 since it's a complete retail game title and not some sort of trimmed down f2p 1v1 game..
Kind of weird to think about though. Reaching masters makes you feel like the 2%, but actually, you're already in the top 2% as long as you're active on ladder (which is what, 5 games a week?)
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Last season, I was placed into masters. Played one ranked game and lost so I was 0-1 last season. Played a match this season, still got placed into masters. I was surprised. I started playing unranked games this season and 90% of the games were anywhere from silver-diamond. I play ranked games and I get placed against high dia/ low masters.
This because unranked is dying and has a terrible player pool?
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Wow, I figured the amount of people truly active on the ladder would be small but the under 20 games stats is almost jaw dropping. Thanks for the research.
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So this explains why a lot of former masters including myself are now diamond, and why everyone was saying Blizzard reduced the cutoff for Master? Does this deflation now mean that master league constitutes a lower percentage of the player base than it did before?
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Canada8155 Posts
On September 21 2013 08:09 Doodsmack wrote:
So this explains why a lot of former masters including myself are now diamond, and why everyone was saying Blizzard reduced the cutoff for Master? Does this deflation now mean that master league constitutes a lower percentage of the player base than it did before?
Yes
And no to the second question, they just decreased the size of master league
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Well I guess that helps justify the fact that two seasons ago I was in diamond playing master league players, then I stopped playing and I was placed in platinum last season, and then I still didn't play and was placed into gold this season. And now I'm stomping people who are in my current "league". That just makes me want to play even less though, because I don't have time to play a ton anymore to get back up to the league I used to be at before I was arbitrarily demoted at the beginning of every season -.-'
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Canada8155 Posts
Yeah i was only getting about 30 games in per season, went from master to diamond this season
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Well this is annoying since I dont really like playing 1:1 but 1:1 dictates placements in teamgames and if I dont keep on playing 20 or so 1:1 games (alot for me since I dont really enjoy it) I'll get worse placements in in teamgames dragging my AT team down. While I guess we'll awalys play our way up to our "real" level pretty fast it's not that fun. This also explains why I faced so "bad" opponents when I did my 2:2 RT placements, apparently my MMR is pretty decayed.
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Very interesting read, thank you both for researching those mechanics behind it
On September 21 2013 07:05 Excalibur_Z wrote:
However, according to my research, only 244, or 0.7%, of Bronze players played more than 20 games last season, compared to 1.5% of Silver, 2.2% of Gold, 2.7% of Platinum, 2.7% of Diamond, and 2.9% of Master players. Overall, 98% of players will not play enough games to offset the maximum amount of MMR decay over the course of a season.
Wow, didn't really expected that. I recently check sc2ranks.com to see, how many people are still playing SCII 1v1 ladder. On the EU server there are around 100.000 accounts placed in a 1v1 league, but it didn't tell you, how many of those accounts only play the placement match and never return to the start of next season. So I guess we'll look at around 2500 active player base with a lots of people who play very, very casually.
That looks quite grim, but i'm still not jumping on the "SCII is dead" train. RTS games are not very popular in these days (nothing new) and I don't see that changing in the near future. As long as I can play my 1v1 / watch tournaments, SCII is aLive for me 
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Well i got decayed from platinum to silver lol.
It took quite a while to get back to platinum and i had 3 to 1 win loss ratio at one moment.
In gold most of my opponents were truly gold players.Ex platinum-diamond players came only when i was on top of my gold division and in platinum.
This MMR decay made things more interesting if you ask me.Maybe even got some inactive players to get back and defend their previous league honor :D
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Only 2.9% of masters doing >20 games ? Any idea how many masters it represents ?
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WCS
