What you don’t know can kill you.

Forget the law of gravity and you’ll have a quick one-way trip off the knife’s edge of Mount Katahdin. Forget the ideal gas law and a pressurized container in your car could explode on a hot day.

Sociology’s laws are subtler than the laws of physics, but they’re no less deadly.

Take Feld’s law, for instance. Twenty-five years ago, sociologist Scott Feld demonstrated that on average, your friends have more friends than you do. This sounds impossible, but it’s true.

Consider the following social network, in which circles represent people and lines represent friendships:

samplenetwork (2)

Some people in this network, like Carol, have more friends than others, like Hal. Some members of this network are friends with very friendly people; Don’s friends have 3.5 friends of their own on average (Carol with 4 friends, Ed with 3). In contrast, the average friend of Carol has just 2.25 friends (Al, Betty and Don with 2 friends each, and Gina with 4).

So far, all of this might sound fairly natural and normal. But as Feld found, things get strange when we consider the overall trend.

Take a look at the table below, which shows the results for each person as well as the overall average for all people. The average person in our network has 2.5 friends. The average person’s average friend has 2.9 friends. That’s Feld’s law.

Friends chart

Go ahead, draw your own social networks and do the math for yourself. You’ll find that Feld’s law holds true for almost any network you can think of. That’s odd, but why should you care?

One reason to care is that Feld’s law explains that feeling many of us have that we’re less popular than our friends. Odds are, you’re right. Don’t take it personally; it’s just the way societies work.

Another reason to care is that Feld’s law is also true for any relationship in which people share something with one another. People share needles in the opiate epidemic facing Maine. People have shared sexual relations since the dawn of humanity. These kinds of sharing can also share deadly viruses like AIDS, hepatitis B and syphilis.

If you’re thinking of sharing a needle, Feld’s law tells us that on average, the people you share needles with share needles with more people than you do. Feld’s law tells us that on average, the people with which you have unprotected sex have unprotected sex with more people than you do. This means that even if you share a needle just once, even if you have unprotected sex just once, your chances of catching a killer virus are disproportionately high.

Understanding invisible social laws can be just as important as understanding invisible physical laws. When you support research to uncover these laws, the life you save just might be your own.

James Cook has been a professor of social science at the University of Maine at Augusta since 2011. Dr. Cook’s primary areas of interest in research and teaching are political organizations, social networks, and social media, specifically applying social network theory to social media in the Maine State Legislature.

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