Happiness is contagious say researchers Nicholas Christakis and James Fowler, author of “Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives.” In a scientific survey they analyzed a network of relationships. In the diagram, happy is yellow, sad is blue, and green is, you guessed it, in between. They found that happiness always spreads from person to person, whereas unhappiness only sometimes spreads between persons.

The scientists base much of their work on the spread of obesity, since obesity can be measured more easily than happiness. Net: We are products of our environment, as in “Tell me who your friends are and I will tell you who you are.”

That helps to explain two things about today’s Princeton Chamber Trade Fair.

1. Why people like to attend. By gathering in large enthusiastic groups, the enthusiasm rubs off on them. Any sales message they are trying to impart is more likely to rub off when everybody is having a good time.

2. Why people like to live and work in the Princeton area. Lots of interesting people live in this neck of the woods. According to Christakis and Fowler, how you act is affected, not just by people you know, but by people who know the people you know.

How’s that for a siren call to a trade fair. It’s at the Westin from 11 to 4 with a social media panel at 9:30 and a Tweet-up at noon. I’ll be there most of the day. Follow the tweets at #prcc