Adventures in Game Theory: Mass Effect 2

The highly successful sequel[1] of BioWare’s action role playing game “Mass Effect”, Mass Effect 2, was released for Windows PC and Xbox 360 in January 2010. The game’s description outlines the features that players can expect:

  • Prepare for a suicide mission to save humanity.
  • Choose between 19 different weapons.
  • Devastating heavy weapons [that] can end a battle in seconds.
  • Recruit a team of the galaxy’s most dangerous operatives.
  • Explore the galaxy –scan planets to uncover unique secret missions.
  • Train and equip your team to survive insurmountable odds.
  • Control your conversation with physical moments of intense action.

(BioWare, 2010)

Mass Effect 2 can be classified as an “Action Role Playing Game” – as it focuses on first person perspective combat and gameplay challenges, but also incorporates the character progression, conversation mechanics and establishment of relationships that features in many Role Playing Games. It is a paidic game, but with a central structure of main quest lines that form the backbone of each act in the story – however the player can complete side quests, travel freely throughout the universe, and explore as they wish.

Game Theory

Game Theory is a field of mathematics that can be used to study a variety of topics, including but not exclusive to games – and is also often used to examine behavioral trends in economics and sociology. “Game theory is about how competitors make optimal choices, and it’s mostly used in politics and economics…” (Koster, 2005)

One aspect of Game Theory, Decision Theory, identifies how and why players decide which choice is optimal. It classifies the risks involved with certain decisions, the strategies undertaken to determine the best possible outcome, and is used to determine this conclusion. In the context of mathematics and economics, statistical methods can be used to facilitate decision-making, such as utilizing probability. (Fisher, 2010)

In games, this optimal choice can be affected by the utility that the player receives from making a decision. This could be rewards or punishments, or a situation which simply has relative preference over other situations that could occur. (Romp, 1997) In most cases players will aim to minimize their losses rather than maximizing the amount gained, and Expectation Analysis can be used to predict strategies and minimize threat. (Packel, 2006) Furthermore, Information Theory can also be used to analyse strategies and distinguish the differences between finite and infinite games – depending on the restrictions on the player’s decision making. (Carse, 1997)

Game Theory in Mass Effect 2

 Mass Effect 2 is a paidic game that allows the player to complete missions in any order they choose – however, it does have a structure to maintain balance and progression – a set of acts that the narrative is set by, and during each act a selection of missions are presented to the player, giving it an aspect of a ludus structure. This demonstrates the fact that “ludus is a form of paidia that operates under a system of rules outlining victory or defeat conditions” (Cristie, 2008).

The player must recruit NPCs[2] to their squad, and can gain loyalty with these characters to affect gameplay – which acts as a form of utility – a tool that helps the player make decisions (Davis, 1997).  The player is provided with a extensive form tree structure (Rapoport, 1999) of strategies to take on, including the Paragon tree and the Renegade tree which will affect their morality, other character’s reactions to the player and future available actions during conversations (Bioware, 2010).

Knowledge of the narrative is withheld from the player to maintain an air of mystery, and the NPC who delivers the main narrative – The Illusive Man – works as a tool of Information Reduction, meaning the player does not know the exact results of their actions until they happen (Leinfellner & Köhler, 1998).

There are many issues with applying Game Theory to Mass Effect 2, as player decisions can have a huge impact on their overall experience of the game. The game features a simplistic form of Resource Management – a feature of game theory that has been used in economics to develop strategies to maintain international fisheries (Munro, 2009) – using which the player must gather in order to upgrade their ship. This must be balanced with the spending of money on other essentials, as many of the squad members will fall in battle during the later stages of the game if the ship is not upgraded enough. This significantly changes the gameplay, and this Information Reduction means the player is unaware of the utility of this decision.

Furthermore, the method by which the player gains loyalty with a team member is by completing a one-time mission, which changes player relationships and squad dynamics. However, should the player lose loyalty with that squad member, which often can be affected by inter-NPC relations, the effect of that utility is lost.

Unintended reactions to player decisions can also occur when the player chooses their conversation options, which add points to their morality for either Renegade or Paragon[3]. Although this separation of the morality scale means no action is unavailable to the player at any time, it also means that it is difficult for the player to assess the strategy they will undertake, or predict the outcome of their decision. All of the above issues are examples of “The Tyranny of Small Decisions” (Kahn, 2007), where seemingly small decisions can result in much larger undesirable outcomes.

In order to improve the game’s design, efforts should be undertaken to minimize “The Tyranny of Small Decisions” (Kahn, 2007). In order to allow players to regain loyalty with other squad members – creating a realistic player experience akin to real-life relationships – a more complex system of loyalty could be implemented, making use of a Bargaining or Negotiation system to influence NPCs. In this case, the Feasibility Set would be the advantages that the player receives from obtaining the NPC’s loyalty, and the Disagreement Point would be the breaking of the NPC’s trust, based on a set of values they should withhold. An example of a bargaining strategy is the “Nash Bargaining Solution”, which suggests players must compromise to find a balance of utility received whether they agree with the other party or not, usually a 50-50 split (Nash, 1950).

Mechanism Design – or Reverse Game Theory (Endriss, 2006) – is a theory which can be applied to games in which the player is unsure of the winning circumstances. For example, if applied to a Role Playing Game such as Mass Effect 2 it is not always easy to tell if the information sources are to be trusted. More than once during the game The Illusive Man changes the information that he tells the player, and this confuses the narrative and gameplay as the player is not sure what their overall goal should be. Using Reverse Game Theory, the player could draw conclusions from The Illusive Man, even though he may be lying. Furthermore, use of more complex Artificial Intelligence trees for the Illusive Man and other informants may give an element of dimensionality, whilst the ability to outwit and interpret the perplexing conversations with The Illusive Man will become another form of Utility.


Using Mass Effect 2 to demonstrate the use of Game Theory in current video games, it is possible to assume that the designers of this series have taken the concepts of Game Theory into account when developing Mass Effect, its environments, gameplay and lore. By doing this, it is ensured that will have a fulfilling game experience, and encouraging them to make optimal choices and decisions throughout their encounter. The use of game theory in the design of Mass Effect has improved the gameplay experience, and although in some cases – such as the unpredictable outcomes of decisions – the gameplay is impeded by its use, research has shown that further implementation of other Game Theory concepts can resolve these issues.

This investigation has identified a few key areas in which Mass Effect 2 could implement Game Theory strategies, but further research is needed to form a complete analysis of the research area. For example, investigating the exploring and research gathering strategies of the player, how and why they should form relationships with individual NPCs, and how developers can encourage the player to traverse a certain path through the game narrative and world in a paidia game. As a sequel – and the last game in the series – is currently in development, an assessment of the series as a whole would provide a thorough analysis of Game Theory being used in a game context, and more specifically from an RPG perspective.

Works Cited

Bioware. (2010). Mass Effect Wiki. Retrieved December 3rd, 2010, from

BioWare. (2010). Official Mass Effect 2 Website. Retrieved November 30th, 2010, from

Carse, J. P. (1997). Finite and Infinite Games. Random House Publishing Group.

Cristie, R. (2008). Proceedings of the 5th Australasian Conference on Interactive Entertainment. The Association for Computing Machinery (ACM) (p. 24). Queensland University of Technology, Brisbane Australia.

Davis, M. D. (1997). Game Theory: A Nontechnical Introduction. Dover Publications.

Endriss, U. (2006). Mechanism Design – Multiagent Systems. Retrieved December 4th, 2010, from University of Amsterdam:–/mas-mechanism-design-4up.pdf#PDF Ebook

Fisher, L. (2010). Rock, Paper, Scissors: Game Theory in Everyday Life: Strategies for Co-operation. Hay House.

Kahn, A. E. (2007). The Tyranny of Small Decisions: Market Failures, Imperfections and the Limits of Economics. International Review for Social Sciences , 23-47.

Koster, R. (2005). Theory of Fun for Game Design. Paraglyph Press.

Leinfellner, W., & Köhler, E. (1998). Game Theory, Experience, Rationality: Foundations of Social Science, Economics and Ethics – In Honor of John C. Harsanyi. Springer.

Munro, G. R. (2009). Game Theory and the Development of Resource Management Policy: The Case of International Fisheries. Environment and Development Economics – Cambridge University Press .

Nash, J. F. (1950). The Bargaining Problem. Econometrica , 155-162.

Neumann, J. v., & Margenstern, O. (2007). Theory of Games and Economic Behaviour. Greenwood Publishing Group (Princeton University Press).

Packel, E. W. (2006). The Mathematics of Games and Gambling. MAA.

Pillis, J. D. (2004). 777 Mathematical Conversation Starters. The Mathematical Association of America.

Quillen, D. (2010). Mass Effect 2 Week One Sales Top 2 Million – Retrieved November 27th, 2010, from

Rapoport, A. (1999). Two-Person Game Theory. Courier Dover Publications.

Romp, G. (1997). Game Theory: Introduction and Applications. Oxford: Oxford University Press.

[1] Mass Effect 2 sold over two million copies worldwide during the first week of release (Quillen, 2010)

[2] NPC in this context refers to a Non-Player Character, in either single or multiplayer games.

[3] “Morality is measured in Mass Effect games by “Paragon” and “Renegade” points. Unlike many contemporary role-playing games, such asBioWare’s Star Wars: Knights of the Old Republic, that represent morality as a single sliding scale of good and evil, Mass Effect keeps track of the Paragon and Renegade points on separate scales. A good action will not make up for an evil one; therefore, being nice occasionally will not stop people from fearing a killer or remove the reputation of an unsympathetic heel, but nor will the occasional brutal action significantly damage the reputation of an otherwise upstanding soldier. This also means there is no gameplay-driven motivation for avoiding a particular type of action.” (Bioware, 2010)


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