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One part of the OP is wrong...365chess.com's free opening database has master & non-master games in one database. But yeah, they are sometimes hard to decipher. In addition to some of the other issues noted above, there are preparation/comfort/psychological effects that influence win rates. For example, many white players are uncomfortable playing the main lines of the French Defense, and play the Exchange Variation in a misguided attempt to take black "out of theory" or "out of their comfort zone". Although the Exchange Variation is symmetrical, and by definition slightly better for white, black actually wins most of these games. Why? Because it is super common, and all French Defense players are very experienced and comfortable with it. Perhaps the white players who chose the exchange variation also tend to be weaker, on average.
Its interesting information...just not the best way to pick an opening repetoir.
Ok I wasn't aware that non-master games were included. But you are right - even though the information can be hard to apply at times, it is fascinating to look at
Another factor to consider is that strong GM's will play main lines against strong opponents, but may deliberately play weaker lines against weaker players in order to get them out of book. Thus bad moves may end up with very good stats. I believe you can see the opponent's average rating in explorers like chesstempo's or in Chessbase the program.
Yeah nice! I didn't think of that. Thanks for the sources too
Just to clarify, it is the performance rating of a move in Chesstempo or Chessbase which tells you if it's just some GM racking up easy points versus weak opponents.
@wayne_thomas OK no worries