Almost everybody has hared about the concept of “Six Degrees of Separation”. Today I want to talk about an even more interesting but related concept: “The Three Degrees of Influence”.

To recapitulate, people are all connected by an average of “Six Degrees of Separation” (your friend is one degree from you, your friend’s friend is two degrees, and so on). An experiment proved this in the 60’s by giving a few hundred people who  lived in Nebraska a letter addressed to a businessman in Boston, more than a thousand miles away. They were asked to send the letter to somebody the knew personally. The goal was to get it to someone they thought would be more likely than they to have a personal relationship with the Boston businessman. The number of hops were tracked. On average, six hops were required.

However, just because we are connected to everyone else by six degrees of separation, doesn’t mean that all these people affect us in the same manner. The spread of influence in social networks obey what is call the Three Degree of Influence Rule.

From Christakis and Fowler Book Connected (p. 28)

“Everything we do or say tends to ripple through our network, having an impact on our friends (one degree), our friends’ friends (two degrees), and even our friends’ friends’ friends (three degrees). Our influence gradually dissipates and ceases to have noticeable effect on people beyond the social frontier that lies at three degrees of separation. Likewise, we are influenced by friends within three degrees of separation but generally not by those beyond.”

This interesting rule applies to wide range of attitudes, behaviors, feelings, etc; and it applies to the spread of phenomena as diverse as political views, weight gain, and happiness.

Among inventors, innovative ideas obey the rule, so that an inventor’s creativity influences his colleagues, his colleagues’ colleagues, and so on.

Word-of-mouth recommendations for everyday concerns (like how to find a good piano teacher or how to find a home or pet) tends to spread three degrees too.

The rule stops at three degrees since, on average, we may not have stable ties to people at four degrees of separation or more.

This rule is so powerful that shapes our everyday behavior and relationships. For example, each happy friend a person has increases that person’s probability of being happy by about 9%. Each unhappy friend decreases it by 7%. Therefore, you want to be closer to happy people. The same applies to obesity or even richness.

People who have obese friends have more chance of being obese since these friends set the expectations of what is acceptable. You are not out of the rule. You can gain weight if your friends do so, since they (and you) set the expectations of what is acceptable and what is not. If you are a man, does this sound familiar “Don’t worry, you’re over 30…”. And it’s worse if your are already married.

Choose not only who your friends are, but also your friends’ friends and so on. That is, choose your network. It will shape your life.