Four studies have tested the association between sense of humour and longevity. One reported that comedians and serious entertainers on average die earlier than authors. Two publications from the Terman Life-Cycle Study reported a negative association. Cheerfulness (sense of humour and optimism) was the index variable in the first study. In the second study, optimism was taken out, but the negative association prevailed. The fourth study reported a 31% reduction of mortality risk among patients with end-stage renal failure provided that they scored above the median on a test of sense of humour.