"Singer studied 141 three- and four-year olds, and found that 65% reported having imaginary playmates. The children who reported having such companions were less aggressive, more cooperative, smiled more, were better able to concentrate, were less frequently bored, and were more linguistically advanced than their companionless cohorts. They were clearly cognizant of the difference between external reality and the worlds of their imagination..." from Invisible Guests by Mary Watkins