When faced with a dilemma or a task that requires cooperation, people can be classified into four basic personality types – optimistic, pessimistic, trusting and envious – scientists have said. They were surprised to find out that most people are "envious", not caring how well they do as long as it is better than everyone else.

This study, published in the journal Science Advances, is based on the principles of Game theory, a branch of mathematics with concrete applications in sociology and economy. The core of this discipline is examining the behaviours of people in social settings, when they have to take decisions and choose or not to cooperate.

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"Those involved are asked to participate in pairs, these pairs change, not only in each round, but also each time the game changes. Depending on the partner, the best option could be to cooperate or, on the other hand, to oppose or betray. In this way, we can obtain information about what people do in very different social situations," one of the authors of the study Anxo Sánchez from the Carlos III University of Madrid, explains.

While major economic theories often portray humans as rational actors, the research suggests behaviours during collaborative games might be more complex and diverse than previously thought – and this should be taken into account when redesigning social and economic policies, and in social exchanges based on cooperation, such as negotiations.

Four personality types

Hunting deer or rabbits

One dilemma presented to the participants went as follows:

When two people are together they can hunt deer, which is more difficult than hunting other prey, but more rewarding if the animal is caught. If people are alone, they can only hunt rabbits, which they are sure to catch. If one person chooses not to hunt the deer, his or her partner is forced to do the same, even if they would have preferred to hunt the deer.

A person belonging to the Envious group will choose to hunt rabbits because he or she will be at least equal to the other hunter, or maybe even better if they catch more animals. The Optimist will choose to hunt deer because that is the best option for both hunters, hoping the other will choose to do the same.

The Pessimist will go for rabbits because that way he or she is sure to catch something, and the hunter who belongs to the Trusting group will cooperate and choose to hunt deer, without a second thought.

In this study, 541 volunteers were recruited and presented with hundreds of social dilemmas and cooperative games, and had the option of collaborating or not with others, based on individual or collective interests. Four personality types were defined based on these social exchanges.

First come the "Optimists" who believe they and their partners are always collaborating to make the best choice for all of them. Then the "Pessimists" are participants who select the options which they view as the lesser of two evils and always try to limit the damage.

The third group is known as the "Trusting group", made up of people who are born collaborators and for whom cooperation is the most important outcome even if they end up losing. Finally, researchers have identified the "Envious group", in which people only care about being the best as individuals.

The researchers then developed a computer algorithm which set out to classify participants to the study in these groups, according to their behaviour during the games. They were able to attribute a personality type to 90% of people. The largest group was the envious – with 30% of participants – which was not what the researchers had been expecting. The three other groups contained roughly 20% of participants each.

This suggests that people are not as rational as theory may predict and some may renounce cooperation to claim individual satisfaction. The researchers believe their results can shed a new light on the mechanisms that drive the collective or individual interest in the processes of negotiation. They could be considered to improve management of business or political reform.