Only Half of Friendships Are Mutual: What the MIT Study Found

Study Finds That Only 50% Of Our Friends Actually Like Us

Are the people you call friends likely to call you a friend back? A 2016 study in PLOS ONE suggests the honest answer is "about half the time". When 84 people rated everyone in a shared university class, they predicted that almost all of their friendships would be returned. In reality, only 53% of the ties were mutual. The gap matters for more than hurt feelings: it shapes how well we can support each other, and who can actually change someone else's behaviour.

What the researchers measured

The paper, "Are You Your Friends' Friend? Poor Perception of Friendship Ties Limits the Ability to Promote Behavioral Change", was written by Abdullah Almaatouq, Laura Radaelli, Alex Pentland and Erez Shmueli and published on 22 March 2016. Pentland is a well-known computational social scientist at MIT's Media Lab.

The main survey group was 84 students, aged 23 to 38, taking an applied management course together. Each person scored every classmate on a six-point scale from 0 to 5. A zero meant they did not know the person, a three meant a friend, and a five meant one of their very best friends. Anything above 2 was treated as a friendship.

The students were also asked a second question: how do you think this person would score you? That simple extra step is what made the study interesting. It let the team compare what people believed about each relationship with what the other side had actually reported.

94% expected, 53% returned

Out of 1,353 friendship nominations, the students expected 1,273 to be returned, or about 94%. Yet when the researchers matched the two sides, only 413 of the 775 friendship ties ran both ways. That is 53%.

Put plainly, most participants assumed that liking someone meant being liked in return, and roughly half of the time that assumption was wrong. The people who were wrong were not unusually lonely or awkward. The misreading was spread across the group.

A class of 84 is a small sample, and the authors knew it. So they checked five other friendship data sets, from MIT phone-tracking studies to large personality surveys. Mutual friendship ranged from 34% to 53% across them. An earlier study of adolescents had found a somewhat higher figure, around 64%. The pattern held: a large share of the friendships people report are one-sided.

Why we misread our friendships

Pentland's explanation, set out in a May 2016 piece for the Harvard Business Review, is self-image. Admitting that a friendship might be one-way is uncomfortable, so the mind fills the gap with the most flattering assumption. If I like you, surely you like me.

A second problem is that "friend" is a slippery word. Writing about the study for The New York Times, the journalist Kate Murphy noticed that even friendship researchers struggle to define it on the spot. One person may mean someone they would phone in a crisis; another may mean a pleasant colleague they chat to at lunch. When two people use different definitions, a mismatch on a 0-to-5 scale is almost guaranteed.

Children often have clearer rules. The young heroes of the Netflix series Stranger Things sum friendship up as loyalty, sharing your best stuff, keeping promises and, above all, not lying. Adult life blurs those lines, and social media adds another layer: a follow, a like or a quick reply can feel like closeness while asking very little of either person.

Ronald Sharp, an English professor at Vassar College who teaches the literature of friendship, put the risk well in Murphy's piece: friendship is "not about what someone can do for you". He argued that treating relationships as an efficient network of contacts makes it harder to know who is really close to us.

One-way ties and the limits of influence

The study's most practical finding came from a fitness experiment run inside MIT's Friends and Family study between October and December 2010. Participants' phones logged their physical activity, and people were paired with "buddies". In one version of the scheme, a person's cash reward depended on how much more active their buddy became, which gave the buddy a reason to apply friendly pressure.

Encouragement worked best when the friendship was mutual. It also worked when the tie ran from the person applying pressure to the person being encouraged, in other words when the encourager considered the other a friend. When only the person being encouraged felt the friendship, the nudges had little effect.

That has an uncomfortable message for marketing and public health campaigns that look for "influencers" with the most connections. As Pentland wrote, people with many social ties are often no better than average at persuading others, because so many of those ties are not returned, or point the wrong way. The team suggested a different strategy: look for tight groups of people who share many mutual friends, since that kind of embedded friendship predicted reciprocity well.

How many close friends can we keep?

The study fits neatly with the work of the British anthropologist Robin Dunbar. In the 1990s he proposed that humans can maintain stable relationships with roughly 150 people, a figure now known as Dunbar's number. Inside that circle he described smaller layers, with an inner core of about five people who receive a large share of our social time, and around 15 who make up our close friends. Dunbar has told reporters that people who claim many more than five intimate friends are probably counting some weaker ties.

The figure of 150 is debated. A 2021 re-analysis in Biology Letters using newer primate data produced widely varying estimates and concluded that a fixed cognitive limit cannot be derived this way. Earlier field studies of real social networks also found larger average circles. What most researchers agree on is the simpler point: deep friendship takes time and attention, and nobody has an unlimited supply of either.

What this means for your own friendships

None of this means half your friends secretly dislike you. A score of 2 instead of 3 can simply mean the other person sees you as a good acquaintance rather than a friend. Different definitions, different stages of life and different amounts of free time all play a part.

Still, the research suggests a few useful habits:

Notice effort, not just warmth. Who calls first, makes plans, or remembers what matters to you? Mutual friendships usually show up as shared effort over time.
Invest in your inner circle. A handful of reciprocal friendships does far more for wellbeing than a long contact list.
Be generous with uncertainty. If a friendship feels lopsided, it may be a mismatch of expectations rather than rejection. A direct, friendly conversation often clears it up.
Choose supporters wisely. If you want help changing a habit, such as exercising more, ask someone who clearly values the relationship too. The study found that is when encouragement works.

The full paper is free to read in PLOS ONE. The video below gives a short overview of the findings.