Scientific American weighs its value:
One benefit of a cheerful character is resilience, a psychic robustness that emotionally buffers people against crises and enables them to see silver linings in major disappointments such as the dissolution of a marriage or the loss of a job. “Humor strengthens the psyche,” Ruch says. In a study published in 1999, he and his colleagues assigned 72 students, all of whom took the STCI, to one of three rooms: a “cheerful” room with large windows, yellow walls, funny posters and colored drapes; a “depressing” room painted black and lit only by a small frosted bulb; and a small “serious” room filled with scientific equipment, books, manuals and presentation posters. The participants performed tasks such as drawing and filling out questionnaires in each of the rooms, as an excuse for spending time in the separate environments. As expected, the ambience of the rooms had a much larger effect on the less cheerful individuals: the depressing and serious rooms put the more humorless students in a worse mood but did not alter the mind-set of the sunnier participants, as measured by a mood test.