Emotions may spread like viruses, but not all emotions spread with the same ease. A study at the Yale University School of Management found that among working groups, cheerfulness and warmth spread most easily, while irritability is less contagious and depression spreads hardly at all. This greater diffusion rate for good moods has direct implications for business results. Moods, the Yale study found, influence how effectively people work; upbeat moods boost cooperation, fairness and business performance.

– Goleman, Boyatzis & McKee, The New Leaders