Guess two thirds
Instructions
You have an integer between 0 and 100.
Winner is whoever comes closest to ^{2}/_{3} of the average of all player's guesses.
Think for a minute, then choose a value.
Evaluations
Number of players:
40 (in two sessions)
Mean guess: 23.75 ±29.4
Winner: 16
Distribution of guesses:
Notes

Impossible to analyze the two sessions individually (missing date entry).

6 players chose the rational solution of zero.

8 players guessed 50 or above.
Comments
Usually the winner is close to 18 or 20 although equilibrium predicts 0.
This means that if all players had been rational, all would have chosen zero.
Written by Christoph Hauert