I just finished reading Connected by Christakis and Fowler. It is an excellent book about social network effects.
Your social network is made up of your friends, family, neighbors and coworkers. According to Christakis and Fowler, what happens in your network affects everything you do. For example, your connections up to 3 degrees of separation away (ie. your friend’s friend’s friend) have been shown to affect you on things like weight gain and loss, emotional contagion, and health.
So being friends of friends with someone who is happy or sick can make you happy or sick. The connection doesn’t seem to go beyond 3 degrees of separation. An example of this was the Farmingham Health study. The Farmingham study tracked thousands of people in a small town in Massachusetts in regards to their cardiac health over 40 years. Fortunately, they also collected a tonne of social data, enabling other researchers to construct an elaborate social network map of the town of Farmingham. What they found was that there was a definite relationship between who participants had fatties in their social network and weight gain.
It make s sense, I guess. When you have a number of overweight people in your reference group, your tolerance and acceptance of obesity goes up. You start to unconsciously eat more, so you can be like your acquaintances. The same thing goes for emotions and just about anything else.
So, chose your friends wisely.