Stage 1 Instructions, All Studies

Appendix

Instructions and stimuli

Stage 1 instructions, all studies

Stage 2 instructions, study 1

Stage 2 instructions, studies 2-3

Stage 2 instructions, study 4

Public good contribution

In- and Out-group regard

Re-analysis considering comprehension

Study 1

Study 2

Study 3

Study 4

Aggregated data

Proving the null

Study effect on in-group and out-group regard

Instructions and stimuli

Stage 1 instructions, all studies

Group Assignment and Game Instructions

In this HIT, you will play a game with other MTurk workers. In this game, we will divide MTurk workers intofivegroups oftenplayers each. The five groups will be labeledA, B, C,D,andE.You will be in Group [5]. All participants, regardless of their group, will receive the same set of instructions.

NEW PAGE

In addition to the payment you each receive for participating in this HIT, you can earn more money in bonus, as follows:

-This game will consist of two Stages: Stage 1 and Stage 2.
-In Stage 1, you and all other players will interact with the other members ofyour own group. In this interaction:

Each member of your group is given 30 cents
Each member of your group decides how many of their 30 cents to contribute to their group’scommon project potand how many to keep for themselves
The total contributions to your group’scommon project potare thendoubledand split evenly among the 10 members of your group

-Thus for every 5 cents you contribute, you get 1 cent back: so no matter what the other group members contribute,you personally lose money on contributing, but it benefits your group as a whole. When everyone contributes everything, your group achieves the largest possible project pot.
-For example:
*If everyone contributes all of their 30 cents, everyone's money will double: each of you will earn 60 cents
*If everyone else contributes their 30 cents, while you keep your 30 cents, you will earn 84 cents, while the others will only earn 54 cents
-The other people are REAL and will really make a decision - there is no deception in this study.

Comprehension Questions

Which group are you in? [A; B; C; D; E]
Who will you interact with in Stage 1? [Nobody; All players; Only players who are in your group; Only players who are outside of your group]
Which contribution earns the highest payoff for your group as a whole? [You contributing 0; You contributing 10; You contributing 20; You contributing 30; All contributions earn the group the same amount]
Which contribution earns the highest payoff for you personally? [You contributing 0; You contributing 10; You contributing 20; You contributing 30; All contributions earn you the same amount]

Stage 2 instructions, study1

Competition (Group A saw the same instructions with the As and Bs swapped):

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn more money.

Remember, you are inGroup B.Your group WILL have the chance to earn more money.All members of your group, including you, have the chance to winan additional 10 centsin bonus.

Your group iscompeting against Group Ato earn a larger project pot andreceivethis bonus.In Stage 2, we will compare your group's project pot to Group A's project pot, and see which group contributed more in total. Ifyour grouphas more than Group A,we will give an extra10 centsin bonusto each member ofyour group. But ifGroup Ahas more, will give the extra 10 cents in bonus to each member of their group.

Social threshold:

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn more money.

Remember, you are inGroup C.Your group WILL have the chance to earn more money.All members of your group, including you,have the chance to winan additional 10 centsin bonus.

Your group isworkingto earn a large enough project pot toreceivethis bonus.In Stage 2, we will see if yourgroup's project pot is large enough by comparing it to aproject pot that Group Apreviously contributed to.Ifyour grouphas more than what Group A previously contributed,we will give an extra10 centsin bonusto each member ofyour group. But ifyour group does not have more than what Group A previously contributed, you will notreceivethe extra bonus.

Control:

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn more money.

Remember, you are inGroup D.Your group will NOT have the chance to earn more money.

Stage 2 instructions, studies 2-3

Competition (Group A saw the same instructions with the As and Bs swapped):

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn more money.

Remember, you are inGroup B.In Stage 2, your group WILL have the chance to earn more money.All members of your group, including you, have the chance to winan additional 10 centsin bonus.

Your group iscompeting against Group Ato earn a larger project pot andreceivethis bonus.In Stage 2, we will compare your group's project pot to Group A's project pot, and see which group contributed more in total.Ifyour grouphas more than Group A,we will give an extra10 centsin bonusto each member ofyourgroup. But if Group A has more than your group, will give the extra 10 cents in bonus to each member of their group.

Thus,your group's payoff will depend on whether you contribute more than Group A, and Group A's payoff will also depend on whether they contribute more than you.

Typically in Stage 1 of this game, groups contribute a total of around 200 (out of a possible 300) cents to the common project pot. So to earn the extra bonus (by contributing more than Group A), your group probably needs to contribute more than around 200 cents in Stage 1.

Social threshold:

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn more money.

Remember, you are inGroup C.In Stage 2, your group WILL have the chance to earn more money.All members of your group, including you,have the chance to winan additional 10 centsin bonus.

Thus,your group's payoff will depend on whether you contribute more than Group A. However, Group A's payoff will not depend on whether they contribute more than you:Group A will get the same payoff regardless of who contributes more.

Typically in Stage 1 of this game, groups contribute a total of around 200 (out of a possible 300) cents to the common project pot. So to earn the extra bonus (by contributing more than what Group A previously contributed), your group probably needs to contribute more than around 200 cents in Stage 1.

Non-Social threshold:

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn more money.

Remember, you are inGroup E.In Stage 2, your group WILL have the chance to earn more money.All members of your group, including you,have the chance to winan additional 10 centsin bonus.

Your group isworkingto earn a large enough project pot toreceivethis bonus.In Stage 2, we will see if yourgroup's project pot is large enough by comparing it to a randomly determined benchmark.Ifyour grouphas more than the benchmark,we will give an extra10 centsin bonusto each member ofyour group. But ifyour group does not have more than the benchmark, you will notreceivethe extra bonus.

Typically in Stage 1 of this game, the randomly determined benchmark requires groups to contribute a total of around 200 (out of a possible 300) cents to the common project pot. So to earn the extra bonus (by contributing more than the benchmark), your group probably needs to contribute more than around 200 cents in Stage 1.

Control:

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn more money.

Remember, you are inGroup D.In Stage 2, your group will NOT have the chance to earn more money.

[Only in Study 3] Typically in Stage 1 of this game, groups contribute a total of around 200 (out of a possible 300) cents to the common project pot. Regardless of what your group contributes in Stage 1, you will NOT have the chance to earn a bonus in Stage 2.

Stage 2 instructions, study 4

Competition (Group A saw the same instructions with the As and Bs swapped):

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn a "gold medal".

Remember, you are inGroup B.In Stage 2, your group WILL have the chance to earn a gold medal.All members of your group, including you, have the chance to be labeled asa gold-medal contributor,denoting that your group contributed a large amount.

Your group iscompeting against Group A to earn a larger project pot and receive gold medals.In Stage 2, we will compare your group's project pot to Group A's project pot, and see which group contributed more in total.Ifyour grouphas more than Group A,we will label each member ofyourgroup as a gold-medal contributor. But if Group A has more than your group, we will label each member of their group asa gold-medal contributor.

Thus,your group's gold medal label will depend on whether you contribute more than Group A, and Group A's gold medal label will also depend on whether they contribute more than you. When you are paid your bonus for this study, you will find out whether you received a gold medal (although the medal does not affect your bonus).

Typically in Stage 1 of this game, groups contribute a total of around 200 (out of a possible 300) cents to the common project pot. So to earn the gold medal (by contributing more than Group B), your group probably needs to contribute more than around 200 cents in Stage 1.

Social threshold:

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn a "gold medal".

Remember, you are inGroup C.In Stage 2, your group WILL have the chance to earn a gold medal.All members of your group, including you, have the chance to be labeled asa gold-medal contributor,denoting that your group contributed a large amount.

Your group isworkingto earn a large enough project pot to receive gold medals.In Stage 2, we will see if yourgroup's project pot is large enough by comparing it to aproject pot that Group Apreviously contributed to.Ifyour grouphas more than what Group A previously contributed,we will label each member ofyourgroup as a gold-medal contributor.But ifyour group does not have more than what Group A previously contributed, you will notbe labeled as a gold-medal contributor.

Thus,your group'sgold medal labelwill depend on whether you contribute more than Group A. However, Group A'sgold medal labelwill not depend on whether they contribute more than you:Group A will get the samegold medal labelregardless of who contributes more. When you are paid your bonus for this study, you will find out whether you received a gold medal (although the medal does not affect your bonus).

Typically in Stage 1 of this game, groups contribute a total of around 200 (out of a possible 300) cents to the common project pot. So to earn the gold medal (by contributing more than Group A), your group probably needs to contribute more than around 200 cents in Stage 1.

Non-Social threshold:

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn a "gold medal".

Remember, you are inGroup E.In Stage 2, your group WILL have the chance to earn a gold medal.All members of your group, including you, have the chance to be labeled asa gold-medal contributor,denoting that your group contributed a large amount.

Your group isworkingto earn a large enough project pot to receive gold medals.In Stage 2, we will see if yourgroup's project pot is large enough by comparing it to a randomly determined benchmark.Ifyour grouphas more than the benchmark,we will label each member ofyourgroup as a gold-medal contributor.But ifyour group does not have more than the benchmark,you will notbe labeled as a gold-medal contributor.

When you are paid your bonus for this study, you will find out whether you received a gold medal (although the medal does not affect your bonus).

Typically in Stage 1 of this game, the randomly determined benchmark requires groups to contribute a total of around 200 (out of a possible 300) cents to the common project pot. So to earn the gold medal (by contributing more than the benchmark), your group probably needs to contribute more than around 200 cents in Stage 1.

Control:

After completing Stage 1, the game will move on to Stage 2. In Stage 2, some groups will have the opportunity to earn more money.

Remember, you are inGroup D.In Stage 2, your group will NOT have the chance to earn more money.

Typically in Stage 1 of this game, groups contribute a total of around 200 (out of a possible 300) cents to the common project pot. Regardless of what your group contributes in Stage 1, you will NOT have the chance to earn a bonus in Stage 2.

Public good contribution

After completing the comprehension questions, participants were reminded of their group label and the nature of the Stage 2 interaction. On the same page as their group label and Stage 2 reminder, they made the public good contribution decision.

In- and Out-group regard

Immediately after participants made their contribution decision, they answered questions about how they would feel, from 1 (very unhappy) to 7 (very happy), about the success of failure of one of their group members:

Imagine that a member ofyourgrouplater completes a different HIT on MTurk. In this HIT, workers receive a bonus, and then can either LOSE the bonus, or WIN more bonus.

How happy would you feel if you found out that the member of your group LOST their bonus? [1 (very happy) – 7 (very unhappy)]

How happy would you feel if you found out that the member of your group WON more bonus? [1 (very happy) – 7 (very unhappy)]

Then, for participants in the competition and social threshold conditions, we asked the same questions about a member of the group they were compared to. In the cases of the control and Non-Social threshold conditions, we asked about Group A, who they had not interacted with.

Now, imagine that a member ofGroup A [Group B for those in Group A]later completes a different HIT on MTurk. In this HIT, workers receive a bonus, and then can either LOSE the bonus, or WIN more bonus.

How happy would you feel if you found out that the member of Group [A or B] LOST their bonus? [1 (very happy) – 7 (very unhappy)]

How happy would you feel if you found out that the member of Group [A or B] WON more bonus? [1 (very happy) – 7 (very unhappy)]

Re-analysis considering comprehension

All the analyses reported in the main text include everyone who participated in the study, independent of whether or not they correctly answered the comprehension questions. In the tables below we report ANOVA results predicting PGG contributions from each study in four columns: 1) all participants; 2) including comprehension as a covariate; 3) excluding those who failed any comprehension questions; and 4) interacting comprehension with condition.

Study 1

Study 1 Comprehension analyses

1 / 2 / 3 / 4
Condition / 4.72*** / 4.75*** / 3.73* / 2.86†
Comprehension / 0.65 / 0.77
Condition X Comprehension / 0.1
Observations / 402 / 402 / 340 / 402
† = p<0.10, * = p<0.05, ** = p<0.01, *** = p<0.001

Table A1. Here we show the effect of condition on contributions from Study 1 including all participants (1), controlling for comprehension (2), excluding non-comprehenders (3), and the factorial interaction between condition and comprehension (4). Our results are largely unaffected by comprehension.

In addition to the series of ANOVAs shown in Table A1 above, we conducted t-tests to compare the control condition to all other conditions and the competition condition with the social threshold condition, excluding participants who failed comprehension questions. We found a significant difference between the control condition (M=0.510, SD=0.453) and all others (M=0.656, SD=0.432), t(338)=2.65, p=0.008. We found no difference between the competition (M=0.643, SD=0.438) and social threshold conditions (M=0.682, SD=0.421), t(255)=0.681, p=0.497.