How common is Multiple Personality Trait in the general public: Is my figure of 30% a wild overestimation or a reasonable guess?

Multiple Personality Trait is what I call multiple personality minus the distress and dysfunction required to make a clinical diagnosis. While there is reason to believe that about 90% of fiction writers have the trait—e.g., Marjorie Taylor’s study of fifty fiction writers found that about 90% had “the illusion of independent agency,” characters that seemed to have minds of their own—there is no study of nonclinical multiple personality in the general public. So is my guess of 30% reasonable?

Rita Carter’s Multiplicity: The New Science of Personality, Identity, and the Self (New York, Little Brown, 2008) argues that having more than one personality is simply the way most people are, that it is human nature. But since she may have multiple personality trait, she seems to feel that if you don’t seem to have it, you probably just won’t admit it.

My guess of 30% is based on four things. First, fiction writers have to come from somewhere. I don’t think that writing fiction gives you multiple personality trait, but that, from people in the general population who have the trait, some people self-select themselves to write fiction. Second, a surprising number of people believe in angels and ghosts, which in some cases might be alternate personalities. Third, multiple personality usually originates to cope with traumatic childhood experiences, which unfortunately are not rare. Fourth, childhood imaginary companions—a phenomenon similar to, and sometimes evolving into, alternate personalities—are, according to the most thorough studies, at least briefly present in the majority of children.

In short, 30% is a reasonable guess.