This study is the latest in a series that Christakis and James Fowler of the University of California, San Diego have conducted to see how habits and feelings move through social networks.
Their earlier studies suggested that obesity, smoking and happiness are contagious.
These studies show why the company we keep is so important.
I would never advocate hanging out around unrealistic people, but those who are essentially negative are as dangerous
as those who are oblivious of the realities around them.