C'era un topic interessante che ne parlava
http://it.reddit.com/r/DotA2/comments/1utoq5/random_facts_about_valve_mmr_clearing_up_the/
- The starting/default MMR is 3000 for unranked mode. This is what it always has been, back when Dota 2 beta just came out and you could get your (unranked) MMR from the console.
- Calibration takes your unranked MMR as a starting point in most cases. Some people don't have an unranked MMR at level >13, because they only play bot games -- the starting point is 3000 for them -- and why there is a calibration system in the first place.
- Unranked MMR made no distinction between solo and party MMR. This is why some "professional" streamers who had 70%+ winrates in unranked MM are now on big losing streaks in solo ranked MM -- their unranked MM was mostly skewed by 5-stack wins. Unranked MM now has a separate hidden solo/party rating, but only with the (recent) introduction of ranked MM.
- The calibration period roughly triples the gains and losses per game compared to games after calibration, with a large weighting on RELATIVE hero performance during calibration. The change from the starting unranked MMR to calibrated MMR can be as high as +/- 700. Your win/loss ratio during calibration is also not as relevant to your percentile performance with a hero in KDA/GPM, stun/slow duration, hero damage dealt and damage taken. The old hero "performance" bars were based on this per-hero percentile ranking. This is also why some people have large losing or winning streaks after calibration is complete (because they only play one or two heros).
- Your team (color) placement in solo ranked MMR is usually independent of your MMR unlike HoN BUT NOT at the very highest MMR levels. Blue/pink is typically highest MMR for games where the average MMR >4500. This is not because Valve places the highest MMR player as blue/pink, but because the matchmaking system places those longest in queue as blue/pink. Those people with high MMRs typically spend the longest time in queue, but you can also spend a long time in queue with odd language/server settings.
- The nominal gain/loss per game is 25 MMR points and is a zero sum between winning and losing parties. If you gained or lost 25 points in a game, Valve's Bayesian system had an even expectation of a 50% win chance for both teams. In games where the Bayesian matchmaking system favors one team to win, the gain/loss can be skewed -- e.g. the favored team who won may only gain 3-5 points, or the underdog team who won may gain 40 points. The Bayesian predictor takes other factors besides MMR, such as hero performance and MMR uncertainty, into account.
- When someone abandons after first blood, the MMR system treats the game as 4v5 in terms of Bayesian expectations (see above point). Because it's now treated as a skewed 4v5 game, the team of 5 may only gain 5-15 points points for their win (if somehow the team of 4 wins, they could gain 40+ points).
Also