What does that tell us – that prisoners take care of each other? Or that they fear reprisals?
Probably not reprisals: they were promised anonymity. It’s really not clear what this result tells us. We knew already that people often co-operate, contradicting the theoretical prediction. We also know, for instance, that economics students co-operate more rarely than non-economists – perhaps because they’ve been socialised to be selfish people, or perhaps because they just understand the dilemma better.
You think the prisoners just didn’t understand the nature of the dilemma?
That’s possible. The students were much better educated and most students had played laboratory games before. Maybe the prisoners co-operated because they were too confused to betray each other.
That seems speculative.
It is speculative, but consider this: the researchers also looked at a variant game in which one player has to decide whether to stay silent or confess, and then the other player decides how to respond. If you play first in this game you would be well-advised to stay silent, because people typically reward you for that. In this sequential game, it was the students, not the prisoners, who were more likely to co-operate with each other by staying silent. So the students were just as co-operative as prisoners but their choice of when to co-operate with each other made more logical sense.
Tim Harford has some relevant comments: