Pizza Game

Background

The Pizza Game is a computer-based behavioral task to assess and quantify cooperative behavior in children and adolescents within the framework of a public goods game (PGG). The task was designed by Jan Keil and colleagues in 2017 to study how prosocial and conditional cooperation habits develop in young people. Keil and colleagues also applied the game to clinical-developmental research to examine how factors like childhood maltreatment affect a young person's willingness to cooperate or prefer risk exploitation.

The basic game premise of the Pizza Game is that three players (the participant and two 'co-players', aka computer personas) want to maximize their number of pizza slices. They can choose to pool an initial number of pizza slices at school (each player decides independently how many slices of pizzas, from 0 to 9, to share), where the teacher would additional slices depending on the number of slices shared at school. The final total number of pizza slices is then divided up and shared equally with each of the three players to enjoy at home. The Pizza Game simulates a classic PPG "social dilemma", where individual self-interest (maximizing your own pizza profit) conflicts with the common good (the more shared pizza slices, the higher the final payout for everyone). For example, if all three players decide to bring all of their 9 slices of pizzas (their total endowment) to school, the teacher adds an additional 13.5 slices (27/2) to the collectively shared 27 slices, bringing the grand total up to 40.5. Diving up the 40.5 pizza slices amongst the three players, yields a total of 13.5 slices for each, which is 4.5 slices more than they started out with. However, if only the player decides to share all their 9 slices while the co-players selfishly keep all theirs safely at home, the player loses slices (final yield: 4.5 slices) while the co-players still gain 4.5 slices for a final yield of 13.5.

The Pizza Game runs three consecutive rounds of games, manipulating the prosocial behavior of the two computer-confederates in each one:

1. Cooperative Strategy: Co-players contribute high amounts of their resources to the common pool.
2. Selfish Strategy: Co-players contribute very little to the shared pool.
3. Divergent Strategy: One co-player acts cooperatively while the other acts selfishly.

The Pizza Game is designed for children and adolescents ages 9 to 16. Depending on the participant's reported age and gender, age and gender appropriate images for the co-players are selected. Ages 9 to 12 as well as ages 13 to 16 play with a different set of images. An optional selfie-maker can be run before the actual game to collect a real image of the participant. If no images are collected, the participant is represented by a generic player icon. In addition, the Millisecond implementation of the Pizza Game provides an 'Avatar' version of the game, in which all players are represented by generic avatars. This version can be run in the absence of definite age or gender information.

Task Procedure

The complete Millisecond Pizza Game starts out with collecting age and gender information of the participant. Based on the responses, one of five appropriate game versions are chosen:

1. Version 1: female participants ages 9-12
2. Version 2: female participants ages 13-16
3. Version 3: male participants ages 9-12
4. Version 4: male participants ages 13-16
5. Version 5: avatar version for anybody else

The Pizza Game starts out with a general game page that offers four buttons: a tutorial button and three game buttons with game 1 running the 'cooperative' co-players, game 2 running the selfish co-players and game 3 running divergent co-players.

At the start of the game, only the tutorial button is active, thus forcing participants to work through it first. The tutorial provides detailed information about the game and works participants through three different scenarios (representing the three possible conditions played by the co-players: cooperative, selfish, divergent).

The tutorial is followed by a generic 'practice' game without actual numbers to familiarize participants with the game procedure. Once the tutorial has been completed, participants are returned to the general game interface where the button for 'game 1' is now activated.

Each of the games runs four rounds for a total of 12 rounds. At the beginning of each game, the current co-players are introduced (each game round works with a different set of players). Then, for each round, participants are asked how many slices of pizzas (selecting from 0,3,6 or 9) they would like to bring to school.

Once all players have made their selections, the pizza slices are pooled on a plate at school where the teacher contribution is added. The teacher contribution is always an additional half of the slices contributed by the players. For example, if the players contribute a total of 12 slices, the teacher will add 6 additional slices for a final total of 18 slices. The final number of pizza slices is divided by three and 'returned' (through animations) to the three players. At the end of the round, a summary of the current round as well as all rounds of the current game is provided. At the completion of the entire game, a scoreboard for each 'player' who played the game is generated. The presented scoreboard table is manipulated in such a way that the participant always ends up as the second highest scorer.

What it Measures

The Pizza Game is a measure of cooperative behavior in a social dilemma situation

Psychological domains

• Social Norms: The unwritten, informal rules that define what is considered acceptable within a specific group
• Self-Interest: The drive to maximize one's own gains, even at the expense of others or regardless of social consequences
• Risk Assessment: Calculating the cognitive risk of betrayal versus the financial reward of cooperation
• Reciprocal Altruism: Evolutionary drive to help others with the expectation that the favor would be returned

Main Performance Metrics

• Number of Shared Slices: the number of shared slices (overall and for each game); main measure of prosocial behavior

Psychiatric Conditions

The Pizza Game has been used in research with the following populations

• Maltreated youths

Test Variations

References

Search Google Scholar for peer-reviewed, published research using the Inquisit Pizza Game.

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Nikiforakis, N. (2008). Punishment and counter-punishment in public good games: Can we really govern ourselves? Journal of Public Economics, 92(1), 91–112. https://doi.org/10.1016/j.jpubeco.2007.04.008

Keil, J., Michel, A., Sticca, F., Leipold, K., Klein, A. M., Sierau, S., von Klitzing, K., & White, L. O. (2017). The Pizzagame: A virtual public goods game to assess cooperative behavior in children and adolescents. Behavior Research Methods, 49(4), 1432–1443. https://doi.org/10.3758/s13428-016-0799-9

Khadjavi, M., Lange, A., & Nicklisch, A. (2017). How transparency may corrupt − experimental evidence from asymmetric public goods games. Journal of Economic Behavior & Organization, 142, 468–481. https://doi.org/10.1016/j.jebo.2017.07.035

Keil, J., Perren, S., Schlesier‐Michel, A., Sticca, F., Sierau, S., Klein, A. M., Steinbeis, N., Klitzing, K., & White, L. O. (2019). Getting less than their fair share: Maltreated youth are hyper‐cooperative yet vulnerable to exploitation in a public goods game. Developmental Science, 22(3), e12765–n/a. https://doi.org/10.1111/desc.12765