"How am I ranked among my peers?"
Overview: MMR as calculated by the site lol-mmr is exclusively based on the wins and losses of the participant players, a comparison of their performance. The amount of LP that is gained or lost depends on the history of the players.
If they are similar in wins/losses then expectation of which side will win will be close to 50% and the award will be normal. If one side has a large history of wins compared to the other side, the expectation is the side with more wins will win, and their award will be smaller than normal. But if they lose then the award to the winning team will be larger than normal.
The Elo rating system is a method for calculating the relative skill levels of players in competitor-versus-competitor games such as chess. It is named after its creator Arpad Elo, a Hungarian-born American physics professor. Elo rating system explained on Wikipedia https://en.wikipedia.org/wiki/Elo_rating_system
lol-mmr uses a similar calculation, explained here: http://blog.lol-mmr.com/2016/03/12/league-legends-mmr-calculator/
