Potential Inaccuracies There is only one issue I have gathered that has strong evidence for it, to following is a direction quote from the playdota member xpforever.
Many systems take into account how close each game was, though we do not know if this is a factor used in Dota 2's matchmaking system. New accounts with few games played tend to have high uncertainty, while older accounts with many games played tend to have low uncertainty.
Similar adjustments are likely to come through continually, as Valve admits this to be an experimental phase in their period.
Since normal and ranked matchmaking are tracked separately, a player who has many normal games will still experience high uncertainty in ranked matchmaking if he or she has only played a few ranked games, and vice versa.
Another common case is playing with a friend who has a higher mmr than you, expecting that it will cause your mmr to go higher. All PvP game modes are available for unranked matches.
I will go step by step so this will be a long guide.