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Background

In evolutionary game theory, one can what kinds of different strategies yield the most payoff to players that play the same game repeatedly. Consider, for instance, the iterated Prisoner's Dilemma.

In any given interaction, individuals can choose to cooperate, which yields a fixed benefit $b$ on their partner at a fixed cost $c$ to themselves, or to defect, bestowing no benefit and paying no cost. Here we will consider only conditional strategies that modify their cooperation in response to their partner’s cooperation.

The players may choose to adopt one of three strategies: 1. cooperate conditionally (CC), 2. deceive tactically (TD), or 3. defect honestly (HD). The CCs aim to cooperate only with other cooperative individuals and not cooperate with defectors, whereas HDs simply always defect. Moreover, the TDs always defect, but attempt to hide that defection from others (by, for instance, waiting until they are unobserved or manipulating their reputation by lying). This deception carries a cost $d$. The CCs will cooperate with HDs in proportion $s$ of their interactions, and will fail to recognize TDs as defectors with probability $q$.

Questions

One could analyse this particular game and show that the evolution of cooperation creates selection pressures that favour adopting tactical deception as a strategy, as McNally et al. (2013) have done in the article linked above.

(Question 1) What I wonder, however, is something different. Suppose one would observe the payoffs of two players playing this game repeatedly, without knowing their strategies beforehand. Are there any methods that would allow you, the observer, to infer (with high probability) which strategies they employ in this iterated Prisoner's Dilemma?

(Question 2) This was a particular example of a game in which players can choose some types of strategies. I am curious whether there is any literature in general - possibly on other games - in which methods are described to reveal the strategies of the players, based on the sequence of payoffs one sees as an outside observer.

Literature and thoughts

With the exception of this paper by Lehre Seip et al. (2016), I have found few examples of articles that focus on identifying strategies by analyzing a sequence of payoffs. Moreover, the aforementioned paper focusses on two quite particular roles in a game: those of leaders and followers.

The subject of leaders and followers in game theory may prompt one to consider the class of Stackelberg games, which also follows a hierarchical dynamic. With regards to question two, I am also interested in identifying leaders and followers, and wonder how the methods to do so differ from those employed in games that are not Stackelberg (so non-hierarchical). So I am interested in role detection in both hierarchical and non-hierarchical games.

Finally, something relevant to consider may be the concept of (Granger) casuality. An example of leader detection employing this concept is described here. However, here technique is applied in the context of time series. I am not sure it has relevance in the context of game theory.

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  • $\begingroup$ Since this is clearly not the usual model of a repeated game (where one reacts to signals, not types), can you write down what formal model you have in mind? $\endgroup$ Commented Jun 9 at 14:40
  • $\begingroup$ I don’t understand the question. If you know the payoffs the players receive then you know the strategies they employed, right? $\endgroup$ Commented Jul 10 at 3:28
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    $\begingroup$ @SamHopkins, you immediately know a player's strategy in some particular instances of sequences of moves and games and facing some particular players. Well, you can't even be sure of it, because there might be some random part in it or some past and hidden states she takes into account that could alter her future moves in a new game that starts with the same moves. But anyway you don't know her strategy if you start over a new game and play some sequence of moves you haven't observed yet. Better, consider there is only one game and one sequence of moves. What's her next move? You don't know. $\endgroup$ Commented Jul 10 at 7:43
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    $\begingroup$ This topic is beautiful. Firstly, modelling a player's strategy in some two- or many-players game must inevitably deal with modelling one-player games as well such as binary sequence with the simplest statistics/finite automata/Turing-complete algorithm that could explain sequences in formal languages, touching upon prediction, information theory, decidability, Occam's Razor, Science. Secondly, as soon as you add some tool or theory to your personal bag to model other players' strategy, you are facing an interesting infinite ladder of enrichments by equiping other players with it too. $\endgroup$ Commented Jul 10 at 8:10

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To answer the second question: there is a paper entitled "Inferring strategies from observations in long iterated Prisoner's dilemma experiments" by E. Montero-Porras et al. (2022). The authors make use of a Hidden Markov Model (HMM) to categorize people's strategies according to their behaviour in the iterated Prisoner's dilemma game.

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