Although it may seem strange, science has a lot to say about our friendships. For example, why we have a limited number of friends. Robin Dunbar , an Oxford anthropologist, proposed his famous number 150: the average number of friendships a person can maintain simultaneously.

These friendships are organized in circles : about five best friends, about ten additional good friends, and another thirty simply friends. The rest up to 150 would be what we call acquaintances.

The importance of friendships in high school

To help understand our friendships, in recent years we have conducted quarterly surveys of high school students in Spain. This is a stage of life in which we not only establish relationships but learn how to do so, so it is particularly interesting. On the other hand, no one can ignore the importance of having a good social climate in our schools and institutes. In this sense, our data is unique in that we have followed students for several years.

In our surveys, conducted during two consecutive academic years, we clearly see the first two circles of best friends and just friends. Being in one or the other leads to relationships being more or less stable, with those with best friends being the longest lasting. Belonging to the same class is one of the key factors in the evolution of friendship.

Little adults

It is interesting to note that adolescents have a friendship structure that is basically like that of adults. In fact, in other studies we have found the same type of networks in both age groups. The most notable difference is that the pace at which these relationships evolve, begin or end, is somewhat faster in young people. It is possible then that the perception of adolescence as a turbulent time is due to the greater emotional impact of these changes.

Interestingly, in all surveys we observed that reciprocal relationships (A names B as “best friend” or “friend” and B names A the same way) are 60% of the total. This is a result that is observed in the vast majority of research and is somewhat surprising: only 60% of those who claim to be someone’s best friend or friend are also chosen by that person in the same category.

However, the average masks great variability. In our surveys there are students who have 80% or 90% reciprocal relationships, but also others who only have 10% reciprocal relationships. It seems clear that the latter are not well placed in the social life of the center , which can be an indicator of relationship problems or even being victims of bullying.

Less ‘enemies’ than friends and more changeable

Bad relationships are much less than good ones, around 10%. Bad relationships are much more changeable than friendships, and in most cases those mentioned in one survey disappear in the next. However, they are important to understand the group structure of the classes, which are detected using computer algorithms. These algorithms identify groups in which there are more relationships within the group than outside, although this does not mean that everyone is friends with everyone. If only friendships are taken into account, algorithms sometimes find a large group in a class. By including bad relationships, a division appears into two groups that coincides with what is perceived by teachers and counselors.

Bad relationships are also important in preventing bullying. One of the indicators that we pass on to counselors so that they can assess a possible intervention is the difference between the numbers of good and bad relationships for each student. Experience shows us that this simple subtraction is often enough to detect students in difficulty.

Predict the relationship between two people

On the other hand, with the data on good and bad relationships between students, it can be predicted whether two of them are friends or enemies. To do this, we have found a number that is calculated based on the contacts they have in common. Basically, it is the number of common friends, plus the number of common enemies, minus the people with whom one has a good relationship and the other a bad one. With that number, the algorithm predicts the relationship between those two people with 90% accuracy.

Our analyzes also confirm the relevance of the theory of social balance to understand the evolution of relationships. This theory states that three people can be friends with each other, or two of them can be friends and enemies of the other. For this reason it is usually summarized by saying that the enemy of my friend is my enemy, and the enemy of my enemy is my friend. In our surveys it is seen that these combinations do appear very frequently, more than we would see at random.

Social atoms

The idea that emerges from these studies is that we behave like “social atoms.” We have a fixed relationship structure, in which people enter and leave over time. This evolution is faster the less intense the relationship is, and is directly influenced by the friends and enemies we have in common with others. On the other hand, when we lose a friend, we notice that “hole” in our structure, and we do not recover until we fill it.

Understanding this structure provides us with very useful data to improve social life in schools. But beyond schools, it is one of the aspects that most influences our health . As Dunbar says in his book Friends , after quitting smoking the best thing we can do for our health is to have friends.

Author Bio: Angel Sanchez Sanchez is Professor of Applied Mathematics at Carlos III University