Yes, it is typically american. For instance, G.W. Bush has an imaginary friend who tells him that he is doing a great job on the war on terror. Usually, imaginary friends disappears at or around age 12, but in some instances, they remain with the person, especially when its IQ is lesser than that of a 12 year old kid. Did I answer your question ?
(Sorry if I went a bit off topic
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Aurel