Radio came out top in the study called 'Media and the Mood of the Nation', commissioned by the Radio Advertising Bureau.

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But nearly 50% of the teens were said to have experienced symptoms of depression or a full-blown mood disorder, according to the study, which was presented on Saturday at an annual meeting of the American Academy of Pediatrics, in New Orleans.

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Anxiety disorders and depression are the most common mental illnesses: 28.8% of the general population will have an anxiety disorder in their lifetime and 20.8% will have a mood disorder, according to a 2005 study published in the Archives of General Psychiatry.

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Previous studies have shown that quick, insightful solutions tend to be more correct than analytic solutions (at least, for the types of tasks in the study), and other studies have shown that a positive mood enhances overall cognitive performance.

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One paper published in 2008 concluded that "the idea that pleasant weather increases people's positive mood in general is not supported by the findings of this study".

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Researchers at Northwestern, in a small study using brain imaging, have found preliminary evidence that being in a positive mood aids the creative process in problem solving.

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The study builds on previous research which has shown the insula is involved in the onset of mood disorders.

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After ten weeks of Tai Chi classes, the study group showed significant improvements in tests of their memory, language, attention, stress, mood and fatigue.

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However, the study did suggest that a failed attempt to seemed to increase anxiety levels by a modest degree among those who had mood disorders.

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