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Do you know who your friends are? Most people don’t, according to a study recently published in the PLoS One.

According to researchers from Tel Aviv University and the Massachusetts Institute of Technology, only around half of the people you call your friends would agree with that judgment. This misunderstanding can lead many to overestimate their influence among their peers and form cooperative relationships.

Social influence isn’t simply about getting the most likes on a Facebook photo from all of your friends. As the study authors note, the ability to persuade plays a role in everything from collective action, be it a political movement or labor rally, to product promotion.

“Individuals commonly assume their affective relationships to be reciprocal by default,”

Two factors play an important role in social influence, reciprocity and directionality.

“Individuals commonly assume their affective relationships to be reciprocal by default,” the authors write. In other words, if I consider you to be my friend, surely you think of me as yours. These assumptions turned out to be wrong about half of the time based on data pulled from self-reported surveys taken by a sample of some 600 college students.

In one survey, for example, each student reported perceptions of their relationships with other participants on a scale ranging from zero to five, with zero standing for “I don’t know this person,” to signifying “One of my best friends.” Ninety-five percent of participants misidentified relationships as reciprocal friendships.

The researchers even used their findings to create a “friendship algorithm,” which predicts reciprocity based on a number of factors, such as total number of friends and the number of friends shared in common between two individuals.

Directionality is linked with reciprocity. Friendships are either reciprocal, which provides more social capital to both parties, or unilateral, in which the amount of influence exerted by an individual depends entirely on the direction of the friendship. The person who misjudges another to be a friend responds more readily to social pressure, while the other tends to be more resistant.

What makes reciprocity so important to social influence is its sense of obligation, according to Influence: Science and Practice by Robert Cialdini. In his explanation of reciprocation, Cialdini refers to exchanging favors, but the concept also applies to relationships. An individual who perceives another as a friend can often experience a feeling of obligation. If that sense of indebtness is missing, as is the case in a unidirectional relationship, cooperation breaks down.

So the next time a friends asks you to do something you’d rather not, ask yourself: Would that person do the same for you? If the answer is no, that individual is probably not your friend.