7 ms·

Resilient cooperators stabilize long-run cooperation in Prisoner’s Dilemma

90 points by mizzao 10y ago

deleted 10y ago
[deleted]
jonathankoren 10y ago
The great thing about these experiments and other experiments in the realm of behavior economics is that that they gather real data about how humans actually behave, rather than the traditional underpinnings of economics and philosophy which are basically, "I really want to believe this is is true, so I'll write a book about it, and then then in the 20th century gussy it up with some straight line graphs." So, people aren't strictly rational actors, and altruism is inherent and beneficial. Which isn't exactly surprising. However I don't hold out hope for evidence-based science to central to socio-economic policy, since it would force wide swaths of the population to give up thier cherished beliefs about how they wish the world works, and instead embrace how the world actually does.
Ninjalicious 10y ago
I didn't read the article but the headline makes me postulate that this is because the optimal individual strategy in Prisoner's Dilemma is tit-for-tat. Respond in kind to every action taken against you. If someone offends, attack, if they offer peace, be peaceful. Nice people will more often offer the olive branch (sub-optimally), so anyone else playing the optimal strategy will offer it back. Over time this probably results in a lower violence rate. Even mean people (also sub-optimal) will get dragged into niceness over time since nice/mean probably changes dynamically.
- andybak 10y ago
  A strategy that could beat tit-for-tat consistently was discovered* but tit-for-tat is still fascinating because it is incredibly simple and is almost the optimal strategy. ( * I think it's this: https://sciencehouse.wordpress.com/2012/09/04/a-new-strategy-for-the-iterated-prisoners-dilemma-game/ https://sciencehouse.wordpress.com/2012/09/04/a-new-strategy... )
  - Ninjalicious 10y ago
    People get mad when you don't read the article.
    - saycheese 10y ago
      (People get mad when you say you didn't read the article, especially in the first sentence; that is they read that, downvote, and don't read the comment.)
- quadrangle 10y ago
  I only skimmed the article, but I'm pretty sure that tit-for-tat as a strategy is not the relevant point. The point is that there are people whose strategy is always-cooperate, and enough of those players in a group results in a situation that will stabilize to having a decent amount of real cooperation. Tit-for-tat might have some similar results but probably would need a greater number of tit-for-tat players for stability versus the critical mass of always-cooperate players needed for stability (my speculation).
MarkMc 10y ago
It seems to me that in countries with systemic corruption there is a huge game of prisoner's dilemma being played, with everyone making the 'wrong' decision. Here's a fascinating quote from a book about Kenyan graft [1]: -------------------- Where does each individual draw the limits of his or her compassion, beyond which duties of kindness, generosity and personal obligation no longer apply? I was raised in a household where my parents drew them in totally different places, according to their very different characters and backgrounds. As an Italian, my mother grew up in a country whose government had given birth to Fascism, formed a discreditable pact with Hitler, and launched itself on a series of unnecessary wars which left Italy occupied and battle-scarred. There then followed a seemingly endless series of short-lived, sleaze-ridden administrations. The experience left her utterly cynical about officialdom. Although she dutifully voted in every election, the malevolence of the system was taken for granted, and she would happily have lied and cheated in any encounter with the state had she believed she could get away with it. But no one worked harder for her fellow man, for in the place of the state she maintained her own support network. An instinctive practitioner of what sociologists call 'the economics of affection', my mother had a circle of compassion drawn to include a collection of lonely acquaintances. She visited their council flats bearing cakes, sent amusing press cuttings to their prison cells, queued at the gates of their psychiatric hospitals. Hers was a world of one-on-one interactions, in which obligations, duties, morality itself, took strictly personal form, and were no less onerous for it. The glow she radiated was life-enhancing, but its light only stretched so far, and beyond lay utter darkness. Protecting one's own was vital, for life had taught her that the world outside would show no mercy. She was not alone in her ability to get things done without the state's involvement. 'Il mio sistema' Italians call it: 'my system'. Italy is, after all, the birthplace of the Mafia, the ultimate of personal 'sistema', and my mother's mindset was instinctively mafioso. My father, in contract, was typical of a certain sort of law-abiding, diffident Englishman for whom a set of impartial, lucid rules represented civilisation at its most advanced. He was raided in a country which pluckily held out against the Germans during the Second World War and then set up the National Health Service in which he spent his career, and his trust in the essential decency of his duly elected representatives was so profound that he was shocked to the core by British perfidy during the Suez crisis, and believed Tony Blair when he said there were weapons of mass destruction in Iraq. When, as an eleven-year-old schoolgirl, I mentioned - with a certain pride - that I usually managed to get home without paying my bus fare, he explained disapprovingly that if everyone behaved that way, London Transport would grind to a halt. Remove the civic ethos, and anarchy descended. A logical man, he saw this as the only practical way of running a complex society. It also, conveniently for an Englishman awkward with personal intimacy, enabled him to engage with his fellow man at a completely impersonal level. Not for him my mother's instinctive charm, the immediate eye contact, the hand on arm. He felt no obligation to provide for nieces and nephews, and had a cousin come up for a job before one of the many appointment boards on which he sat, he would have immediately excused himself. Nothing could be more repugnant to him than asking a friend to bend the rules as a personal favour. What need was there for a rival, alternative sistema, if the existing arrangement of rights and duties already delivered? My father's world view was typically northern European. My mother's characteristically Mediterranean approach would have made perfect sense to any Kenyan. In an 'us-against-the-rest' universe, the put-upon pine to belong to a form of Masonic lodge whose advantages are labelled 'Members Only'. In the industrialised world, that 'us' is usually defined by class, religion, or profession. In Kenya, it was inevitably defined by tribe [1] https://www.amazon.com/Its-Our-Turn-Eat-Whistle-Blower/dp/0061346594 https://www.amazon.com/Its-Our-Turn-Eat-Whistle-Blower/dp/00...
saycheese 10y ago
Resilient players, regardless of if they are cooperators or not would obviously add long-term stability; to me, this reads as adding stability creates stability. Majority of players are do not express resilient behaviors, regardless of the impact on them; that is they are random, unable to create a consistent valid strategy, etc. - it is not that they are just greedy, since if that were the case, the system dynamics would be much more stable.
- jakeargent 10y ago
  I'd wager that resilient defectors would not create long-term stable cooperation. They might create stable defection, so in that way adding stability would create stability. But only one of those stable outcomes is actually desirable.
  - saycheese 10y ago
    My guess is there's a relationship between the duration to reach stability and how soon after the "fake" players are removed.
- marcosdumay 10y ago
  It's not obvious that adding a minority if stable players will stabilize the overall game. It was not surprising in face of what was previously known, but it was not obvious either.
  - mizzao 10y ago
    When designing this experiment, we were pretty sure that cooperation would break down altogether based on what people had previously tried. That it didn't and resembles more what we see in the real world (things generally work and people don't stab each other in the back) was not obvious. A general challenge in doing social science research is that once you present a new result, someone will always claim that it was obvious because of X. What they don't see was that there was a Y that could have plausibly explained an entirely different result. Once we've shown which of X or Y is more likely, the world updates, but it was not obvious to begin with. My collaborator Duncan Watts (one of the pioneers in the field of network science) has written a book about this phenomenon: Everything is Obvious, Once You Know the Answer.
oli5679 10y ago
In case anyone wants a primer on the prisoner's dilemma: Suppose both you and a partner get arrested whilst trying to rob a bank. Without a confession from one of you, the police can only convict you of a minor offense (say trespassing). The police place you in different cells, and offer you both the following bargain. If you confess to the robbery, and your partner does not, you get a complete pardon, and your partner gets a full sentence (say 120 months in jail). If you both confess, you get a slightly reduced 100 months in jail. Finally, if you both remain silent then each gets a 3 month sentence for trespassing. You both now have this tension between individual and collectively optimal action. Your personal sentence is smaller (independent of what your partner does) after confessing, but you both benefit from coordinating to not confess. You can draw the payoffs in a matrix (left is row player and right is column player) to visualise this. c c' c 100,100 0,120 c' 120, 0 3,3 This tension applies to lots of other interactions (e.g. firms colluding to restrict output, communities collaborating to maintain public goods, neighbours not pissing each other off by throwing massive parties). Even if there is a repeated interaction for a finite amount of time, you can expect rational self-interested agents to be unable to collaborate in the final period. This means they have no way of punishing in the penultimate round, and so by induction you would expect 'unravelling' to non-cooperation right from the beginning. This paper found that a subset of the population appearing not to be self-interested was sufficient to prevent this complete unravelling. Even a selfish player may wish to collaborate in early interactions if there is a high enough chance that they won't be immediately punished. https://en.wikipedia.org/wiki/Prisoner's_dilemma https://en.wikipedia.org/wiki/Prisoner's_dilemma
- thilmo 10y ago
  When I was a kid and I read about the Prisoner's dilemma in the context of morality, I was always confused. Surely the moral thing is to confess if you're guilty. If you're guilty, and your accomplice is guilty, the right thing to do is confess to the police so that you can be rightfully punished. As an adult I understand that this isn't the point of the story, and the police-and-prisoners aspect of the story is completely extraneous to the point trying to be made. Still, I can't help but think that the police-and-prisoners is a bad example of the broader point, since there's always a third set of interests (that of the police, and of society in general) which is callously (and immorally) tossed aside in the phrasing of the problem.
coderdude 10y ago
looks at TV selling me various pocket knives reads a bunch of people who think they know what they're talking about Is there a place in between for those who don't care about armchair intellectuals? I just want to know. Because a whole lot of basically retards made HN their new home so I'm curious. I'm the only person who noticed, I'm sure.
- andybak 10y ago
  Maybe stick around here but don't click on things that don't interest you? I think the Prisoner's Dilemma is one of the most interesting abstract ideas I've come across and it feeds into my thoughts about morality and human society. My interest in it is because I think it matters I fully admit that I probably "don't know what I'm talking about" but it's not for want of trying. My interest is sincere. Is your cynicism?
  - coderdude 10y ago
    I don't think you're the target of my cynicism. I think you're a dick.
    - andybak 10y ago
      I still stand by my criticism of your cynicism. It was pointless sneering. Either ignore people or educate them.
      - deleted 10y ago
        [deleted]
    - dang 10y ago
      We've banned this account for violating the HN guidelines. If you don't want it to be banned, you're welcome to email hn@ycombinator.com and make this right. We don't like to ban longstanding participants, but you know HN well enough to know that you can't comment like this here. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newswelcome.html https://news.ycombinator.com/newswelcome.html
sinan_si 10y ago
Similar research to whom anyone interested in these topics : https://www.researchgate.net/publication/303656078_The_Dose_Makes_The_Cooperation https://www.researchgate.net/publication/303656078_The_Dose_...
- saycheese 10y ago
  Resilent cooperation is intentional, but cooperating based on a lack of memory is not - guess the question is if it matters if the source of constant behavior matters, and if so, why?
  - Nomentatus 10y ago
    I certainly presume that it matters because the other player must have a theory of mind, and see a string of non-cooperative plays as an intentional penalty, and therefore predictive; that is something said other player can control by behaving better themselves in future.
mizzao 10y ago
Lead author of the paper here; AMA. The main novelty about this work is that we had 100 people play repeated PD for a month instead of <1 hour which is typical in behavioral experiments, in an attempt to make rather stylized cooperation experiments in the lab closer to real life (admittedly, it is still only a small step.) The findings can be summarized in a sentence as "a minority of nice people can make everyone better off."
- vmarsy 10y ago
  Hi, interesting findings! You say as a summary : > a minority of nice people can make everyone better off Was it possible for you to identify the "nice people" group vs the other group? If yes, overall which group was better off ? Once the non nice people start cooperating, i guess you can't make the difference between a nice person and a non nice one
  - mizzao 10y ago
    Yes, in our paper, we identified the "nice" group versus the other group. The nice group is significantly worse off, but (see https://news.ycombinator.com/item?id=13509853 https://news.ycombinator.com/item?id=13509853) still better off than they would be in the world if they weren't being nice. We can tell the difference between the two types of people, because the nice people never defect first. Finally, with regard to identifying these types in general, one could use the (very large) dataset from this experiment to train a simulated agent that plays against a human, and quickly determine which type they fall into.
- ianai 10y ago
  But what cost do they incur? Is it made up for in some way to them?
  - mizzao 10y ago
    See my comment at https://news.ycombinator.com/item?id=13509853 https://news.ycombinator.com/item?id=13509853.
- 10y ago

90 points by mizzao 10y ago

deleted 10y ago

[deleted]

The great thing about these experiments and other experiments in the realm of behavior economics is that that they gather real data about how humans actually behave, rather than the traditional underpinnings of economics and philosophy which are basically, "I really want to believe this is is true, so I'll write a book about it, and then then in the 20th century gussy it up with some straight line graphs." So, people aren't strictly rational actors, and altruism is inherent and beneficial. Which isn't exactly surprising. However I don't hold out hope for evidence-based science to central to socio-economic policy, since it would force wide swaths of the population to give up thier cherished beliefs about how they wish the world works, and instead embrace how the world actually does.

Ninjalicious 10y ago

I didn't read the article but the headline makes me postulate that this is because the optimal individual strategy in Prisoner's Dilemma is tit-for-tat. Respond in kind to every action taken against you. If someone offends, attack, if they offer peace, be peaceful. Nice people will more often offer the olive branch (sub-optimally), so anyone else playing the optimal strategy will offer it back. Over time this probably results in a lower violence rate. Even mean people (also sub-optimal) will get dragged into niceness over time since nice/mean probably changes dynamically.

andybak 10y ago
A strategy that could beat tit-for-tat consistently was discovered* but tit-for-tat is still fascinating because it is incredibly simple and is almost the optimal strategy. ( * I think it's this: https://sciencehouse.wordpress.com/2012/09/04/a-new-strategy-for-the-iterated-prisoners-dilemma-game/ https://sciencehouse.wordpress.com/2012/09/04/a-new-strategy... )
- Ninjalicious 10y ago
  People get mad when you don't read the article.
  - saycheese 10y ago
    (People get mad when you say you didn't read the article, especially in the first sentence; that is they read that, downvote, and don't read the comment.)
quadrangle 10y ago
I only skimmed the article, but I'm pretty sure that tit-for-tat as a strategy is not the relevant point. The point is that there are people whose strategy is always-cooperate, and enough of those players in a group results in a situation that will stabilize to having a decent amount of real cooperation. Tit-for-tat might have some similar results but probably would need a greater number of tit-for-tat players for stability versus the critical mass of always-cooperate players needed for stability (my speculation).

MarkMc 10y ago

It seems to me that in countries with systemic corruption there is a huge game of prisoner's dilemma being played, with everyone making the 'wrong' decision. Here's a fascinating quote from a book about Kenyan graft [1]: -------------------- Where does each individual draw the limits of his or her compassion, beyond which duties of kindness, generosity and personal obligation no longer apply? I was raised in a household where my parents drew them in totally different places, according to their very different characters and backgrounds. As an Italian, my mother grew up in a country whose government had given birth to Fascism, formed a discreditable pact with Hitler, and launched itself on a series of unnecessary wars which left Italy occupied and battle-scarred. There then followed a seemingly endless series of short-lived, sleaze-ridden administrations. The experience left her utterly cynical about officialdom. Although she dutifully voted in every election, the malevolence of the system was taken for granted, and she would happily have lied and cheated in any encounter with the state had she believed she could get away with it. But no one worked harder for her fellow man, for in the place of the state she maintained her own support network. An instinctive practitioner of what sociologists call 'the economics of affection', my mother had a circle of compassion drawn to include a collection of lonely acquaintances. She visited their council flats bearing cakes, sent amusing press cuttings to their prison cells, queued at the gates of their psychiatric hospitals. Hers was a world of one-on-one interactions, in which obligations, duties, morality itself, took strictly personal form, and were no less onerous for it. The glow she radiated was life-enhancing, but its light only stretched so far, and beyond lay utter darkness. Protecting one's own was vital, for life had taught her that the world outside would show no mercy. She was not alone in her ability to get things done without the state's involvement. 'Il mio sistema' Italians call it: 'my system'. Italy is, after all, the birthplace of the Mafia, the ultimate of personal 'sistema', and my mother's mindset was instinctively mafioso. My father, in contract, was typical of a certain sort of law-abiding, diffident Englishman for whom a set of impartial, lucid rules represented civilisation at its most advanced. He was raided in a country which pluckily held out against the Germans during the Second World War and then set up the National Health Service in which he spent his career, and his trust in the essential decency of his duly elected representatives was so profound that he was shocked to the core by British perfidy during the Suez crisis, and believed Tony Blair when he said there were weapons of mass destruction in Iraq. When, as an eleven-year-old schoolgirl, I mentioned - with a certain pride - that I usually managed to get home without paying my bus fare, he explained disapprovingly that if everyone behaved that way, London Transport would grind to a halt. Remove the civic ethos, and anarchy descended. A logical man, he saw this as the only practical way of running a complex society. It also, conveniently for an Englishman awkward with personal intimacy, enabled him to engage with his fellow man at a completely impersonal level. Not for him my mother's instinctive charm, the immediate eye contact, the hand on arm. He felt no obligation to provide for nieces and nephews, and had a cousin come up for a job before one of the many appointment boards on which he sat, he would have immediately excused himself. Nothing could be more repugnant to him than asking a friend to bend the rules as a personal favour. What need was there for a rival, alternative sistema, if the existing arrangement of rights and duties already delivered? My father's world view was typically northern European. My mother's characteristically Mediterranean approach would have made perfect sense to any Kenyan. In an 'us-against-the-rest' universe, the put-upon pine to belong to a form of Masonic lodge whose advantages are labelled 'Members Only'. In the industrialised world, that 'us' is usually defined by class, religion, or profession. In Kenya, it was inevitably defined by tribe [1] https://www.amazon.com/Its-Our-Turn-Eat-Whistle-Blower/dp/0061346594 https://www.amazon.com/Its-Our-Turn-Eat-Whistle-Blower/dp/00...

saycheese 10y ago

Resilient players, regardless of if they are cooperators or not would obviously add long-term stability; to me, this reads as adding stability creates stability. Majority of players are do not express resilient behaviors, regardless of the impact on them; that is they are random, unable to create a consistent valid strategy, etc. - it is not that they are just greedy, since if that were the case, the system dynamics would be much more stable.

jakeargent 10y ago
I'd wager that resilient defectors would not create long-term stable cooperation. They might create stable defection, so in that way adding stability would create stability. But only one of those stable outcomes is actually desirable.
- saycheese 10y ago
  My guess is there's a relationship between the duration to reach stability and how soon after the "fake" players are removed.
marcosdumay 10y ago
It's not obvious that adding a minority if stable players will stabilize the overall game. It was not surprising in face of what was previously known, but it was not obvious either.
- mizzao 10y ago
  When designing this experiment, we were pretty sure that cooperation would break down altogether based on what people had previously tried. That it didn't and resembles more what we see in the real world (things generally work and people don't stab each other in the back) was not obvious. A general challenge in doing social science research is that once you present a new result, someone will always claim that it was obvious because of X. What they don't see was that there was a Y that could have plausibly explained an entirely different result. Once we've shown which of X or Y is more likely, the world updates, but it was not obvious to begin with. My collaborator Duncan Watts (one of the pioneers in the field of network science) has written a book about this phenomenon: Everything is Obvious, Once You Know the Answer.

oli5679 10y ago

In case anyone wants a primer on the prisoner's dilemma: Suppose both you and a partner get arrested whilst trying to rob a bank. Without a confession from one of you, the police can only convict you of a minor offense (say trespassing). The police place you in different cells, and offer you both the following bargain. If you confess to the robbery, and your partner does not, you get a complete pardon, and your partner gets a full sentence (say 120 months in jail). If you both confess, you get a slightly reduced 100 months in jail. Finally, if you both remain silent then each gets a 3 month sentence for trespassing. You both now have this tension between individual and collectively optimal action. Your personal sentence is smaller (independent of what your partner does) after confessing, but you both benefit from coordinating to not confess. You can draw the payoffs in a matrix (left is row player and right is column player) to visualise this. c c' c 100,100 0,120 c' 120, 0 3,3 This tension applies to lots of other interactions (e.g. firms colluding to restrict output, communities collaborating to maintain public goods, neighbours not pissing each other off by throwing massive parties). Even if there is a repeated interaction for a finite amount of time, you can expect rational self-interested agents to be unable to collaborate in the final period. This means they have no way of punishing in the penultimate round, and so by induction you would expect 'unravelling' to non-cooperation right from the beginning. This paper found that a subset of the population appearing not to be self-interested was sufficient to prevent this complete unravelling. Even a selfish player may wish to collaborate in early interactions if there is a high enough chance that they won't be immediately punished. https://en.wikipedia.org/wiki/Prisoner's_dilemma https://en.wikipedia.org/wiki/Prisoner's_dilemma

thilmo 10y ago
When I was a kid and I read about the Prisoner's dilemma in the context of morality, I was always confused. Surely the moral thing is to confess if you're guilty. If you're guilty, and your accomplice is guilty, the right thing to do is confess to the police so that you can be rightfully punished. As an adult I understand that this isn't the point of the story, and the police-and-prisoners aspect of the story is completely extraneous to the point trying to be made. Still, I can't help but think that the police-and-prisoners is a bad example of the broader point, since there's always a third set of interests (that of the police, and of society in general) which is callously (and immorally) tossed aside in the phrasing of the problem.

coderdude 10y ago

looks at TV selling me various pocket knives reads a bunch of people who think they know what they're talking about Is there a place in between for those who don't care about armchair intellectuals? I just want to know. Because a whole lot of basically retards made HN their new home so I'm curious. I'm the only person who noticed, I'm sure.

andybak 10y ago
Maybe stick around here but don't click on things that don't interest you? I think the Prisoner's Dilemma is one of the most interesting abstract ideas I've come across and it feeds into my thoughts about morality and human society. My interest in it is because I think it matters I fully admit that I probably "don't know what I'm talking about" but it's not for want of trying. My interest is sincere. Is your cynicism?
- coderdude 10y ago
  I don't think you're the target of my cynicism. I think you're a dick.
  - andybak 10y ago
    I still stand by my criticism of your cynicism. It was pointless sneering. Either ignore people or educate them.
    - deleted 10y ago
      [deleted]
  - dang 10y ago
    We've banned this account for violating the HN guidelines. If you don't want it to be banned, you're welcome to email hn@ycombinator.com and make this right. We don't like to ban longstanding participants, but you know HN well enough to know that you can't comment like this here. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newswelcome.html https://news.ycombinator.com/newswelcome.html

sinan_si 10y ago

Similar research to whom anyone interested in these topics : https://www.researchgate.net/publication/303656078_The_Dose_Makes_The_Cooperation https://www.researchgate.net/publication/303656078_The_Dose_...

saycheese 10y ago
Resilent cooperation is intentional, but cooperating based on a lack of memory is not - guess the question is if it matters if the source of constant behavior matters, and if so, why?
- Nomentatus 10y ago
  I certainly presume that it matters because the other player must have a theory of mind, and see a string of non-cooperative plays as an intentional penalty, and therefore predictive; that is something said other player can control by behaving better themselves in future.

mizzao 10y ago

Lead author of the paper here; AMA. The main novelty about this work is that we had 100 people play repeated PD for a month instead of <1 hour which is typical in behavioral experiments, in an attempt to make rather stylized cooperation experiments in the lab closer to real life (admittedly, it is still only a small step.) The findings can be summarized in a sentence as "a minority of nice people can make everyone better off."

vmarsy 10y ago
Hi, interesting findings! You say as a summary : > a minority of nice people can make everyone better off Was it possible for you to identify the "nice people" group vs the other group? If yes, overall which group was better off ? Once the non nice people start cooperating, i guess you can't make the difference between a nice person and a non nice one
- mizzao 10y ago
  Yes, in our paper, we identified the "nice" group versus the other group. The nice group is significantly worse off, but (see https://news.ycombinator.com/item?id=13509853 https://news.ycombinator.com/item?id=13509853) still better off than they would be in the world if they weren't being nice. We can tell the difference between the two types of people, because the nice people never defect first. Finally, with regard to identifying these types in general, one could use the (very large) dataset from this experiment to train a simulated agent that plays against a human, and quickly determine which type they fall into.
ianai 10y ago
But what cost do they incur? Is it made up for in some way to them?
- mizzao 10y ago
  See my comment at https://news.ycombinator.com/item?id=13509853 https://news.ycombinator.com/item?id=13509853.
10y ago