On the average move number of a chess game

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The question on the average move number of a chess game occurs frequently in online chess communities (fi. Yahoo, Chess Stack Exchange, Schachfeld). Easiest is to present some statistics from large databases. These are the ChessBase Mega Database 2015 that contains around 6 million games from human players, the ChessBase Correspondence Database 2013 containing around one million games from postal, e-mail and server chess (but no quickplay server games), and a database of around 4 million computer games played on Schach.de recorded by Michael Wäsch. Unfortunately Wäsch's databases are not offered for download any longer. The diagrams were generated employing ChessBase 12.

The contents of MegaBase 2015. At least one player is human. Long games and games between strong players are overrepresented. All games were played over the board.
The length of games in MegaBase 2015. The average move number is 38. There are peaks around the usual time limits for the 40th and the 60th move due to tactical blunders.
The contents of the database of correspondence games by humans (no quick server games).
The average length of corresponence games is 33. There are no peaks at time-limits although they are common in correspondence chess.
The contents of the database of computer vs. computer Internet games.
The average length of computer games is 64. Games usually are not suddenly finished by surprising tactical shots. Intermittent time-limits are not common in server games.
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