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When does a Lichess player experience a new move on average?

AnalysisOpening
How often and how deep do normal amateur games go before they face a new position and are “out of their book”?

I decided to take a look into the data and extracted 207 games from the latest Monthly Classical Arena on Lichess. I then made a Python script that looked up the first new position in the players opening explorer.

I decided to look at classical games since I believe people are more likely to play according to theory in a classical tournament compared to a bullet game. The data was then saved to a Google Sheet so I could make some diagrams for you.

Distribution

The average player had a new position after 5,7 full moves, while the longest game one had in the analyzed games was 20 moves deep. The top of the diagram is around move 5 and then falls after move 6. From a mathematical perspective, it makes sense since after 6 full moves we have hit 62 quadrillion possible chess game variations.

If we look at the games and account for rating and its effect we get the following diagram.

Diagram 2
It is pretty clear that there is not a huge correlation between having a high rating and getting deep into known territory. One factor is that lower-rated players might deviate from theory early or maybe it is just normal to be “out-of-book” between moves 5 and 10.

However, we can see that when we reach the ratings around 1700-1800 Lichess Classical more games begin to go deeper and beyond move 10.

Black vs White
If we look at the influence of color it looks like Black is sooner arrives at a new position compared to the White side. One explanation could be that chess players are switching more with Black and playing the same with White.

Finally, I took a look at the 20 games that went the longest before deviating from an earlier game they had played vs 20 games where the players had a fresh position after move 1 or 2. The top scored 14/20 points while the bottom scored 8/20 points, so it might be useful to know the position after all.

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