File:Chess firstMove.png

English: This was made for the Chess Opening Theory wikibook and corresponds to the data there. These numbers are the average of 5 different chess game databases, which are the following:

• 365Chess.com's 'big'
• Chess Tempo's 'all'
• chessgames.com
• Lichess's 'masters'
• Lichess's 'Lichess database'

365Chess.com and Chess Tempo seem to have many older games (pre-Korean War) that are lacking from Lichess (masters) and chessgames.com. Lichess's (unnamed non-masters) database has data from club-level players (presumably played on the Lichess website?) which apparently can behave quite differently from masters. These are percentages (that is, probability times 100). Since four of the game databases are of very strong players, these numbers are biased toward how very strong players play, which is consistent with how these descriptive statistics are mentioned in many chess books (probably because the books consider this the best way to play the game). However, in a full scientific and anthropological description of the way chess is played in real life, the more usual player should be included, which is why a single club player database is added into the average. Nonetheless, the average is still biased toward strength and more recent trends.