Suicide victims often have low levels of serotonin, a brain chemical that helps to regulate mood, says Morton Silverman, a professor of psychiatry at the University of Chicago and editor of the Journal of Suicide.

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He is a consulting professor of Computer Science at Stanford University and editor-in-chief of the Journal of the Association of Computing Machinery.

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Marcia Angell, a lecturer at Harvard University, former editor of The New England Journal of Medicine and author of The Truth About Drug Companies, wrote in an e-mail that ghostwriting practices are "evidently very common" in medicine.

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