Economic games on the internet:
the effect of $1 stakes
Ofra Amir, David G. Rand and Ya’akov (Kobi) Gal
Background –
Amazon Mechanical Turk
2
Background –
Amazon Mechanical Turk
3
Motivation –
experiments with online markets
• Fast, cheap, low effort
• Incentive compatible
• Cross-cultural
4
But aren’t the stakes too low?
• Payments on MTurk are usually low
• Previous studies found quantitative agreement
between low-stakes games on Mturk and highstakes games in the lab
[Suri & Watts 2011; Horton Rand Zeckhauser 2011]
• Contributions of the current study:
– Testing, within one consistent experimental platform,
whether having $1 stakes matters on Mturk
– Comparing the effect of stakes on MTurk to the effect
of stakes in physical labs
5
Experimental Design
• Four canonical economic games –
–
–
–
–
dictator game
public goods game
ultimatum game
trust game
• Two payoff conditions:
– stakes condition
– no-stakes condition
• 1129 subjects, each assigned randomly to one of
the four games and one of the two conditions.
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Related work – the effect of stakes
• Dictator Game (Forsythe, 1991; Carpenter et al., 2005)
– Significant difference in decisions between stakes and no stakes
• Public goods game (Kocher, 2008)
– No significant difference in contributions when raising stakes
• Ultimatum Game (Forsythe, 1991; Carpenter et al., 2005; Hoffman et al. 1996)
– No significant difference in offers between stakes and no stakes
– Player 2 rejection rate – No difference \ decreases when raising stakes
• Trust Game (Johansson-Stenman et al., 2005; Sutter & Kocher, 2007)
– No effect in behavior \ Decrease in fraction sent when raising stakes
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– No change in fraction returned by the trustee
Results - Dictator game
Player 1 transfer
• Mean transfers of player 1 (stakes condition transferred 10
units less on average)
Stakes
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No Stakes
Dictator game
• Distribution of transfers
(sig. difference, p-value=0.022)
Stakes
No Stakes
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Public goods game
Contribution
• Mean contribution to the public goods, possible contribution
between 0-40
Stakes
10
No Stakes
Public goods game
• Distribution of contributions
(no sig. difference, p-value=0.656)
Stakes
No Stakes
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Ultimatum game – player 1
Offer
• Mean player 1 offers
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Stakes
No Stakes
Ultimatum game – player 1
• Distribution of player 1 offers
(no sig. difference, p-value=0.1659)
Stakes
No Stakes
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Ultimatum game – player 2
Minimum
Accepted Offer
• Minimum accepted offer (p-value= 0.1941)
Stakes
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No Stakes
Ultimatum game – player 2
Rejection
probability
• Probability to reject by player 1 offer
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Fraction offered
Trust game – player 1
Transfer
• Means of player 1 transfers, possible values between 0-40
Stakes
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No Stakes
Trust game – player 1
• Distribution of player 1 transfers
(no sig. difference, p-value=0.3863)
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Trust game – player 2
Fraction returned
• Fraction returned by player 2
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Fraction transferred by player 1
Comparison with labs results
• Dictator game:
Real money: mean = 0.332
Hypothetical: mean = 0.44
616 studies
from Engel
2010
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Comparison with labs results
• Trust game – player 1:
Real money: mean = 0.58
Hypothetical: mean = 0.551
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Fraction sent by P1
143 studies
from Johnson
& Mislin
2010
Comparison with labs results
• Trust game – player 2:
Real money: mean = 0.47
Hypothetical: mean = 0.45
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Fraction returned by P2
143 studies
from Johnson
& Mislin
2010
Summary
• Significant decrease in transfers in Dictator Game when
using $1 stakes compared to no stakes
• No effect of stakes in public goods, ultimatum game and
trust game
• Consistent with previous lab studies that used higher
stakes
• Supports findings from replication studies which validated
results of experiments run on MTurk
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Questions?
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