Paracosms were first noted by the late Robert Silvey, a pioneer in audience research for the British Broadcasting Corporation (BBC) in England; his 1977 article recounts his own experience. Silvey later joined with psychiatrist Stephen A. MacKeith to begin gathering research about others who had similar paracosm experiences. Silvey died in 1981, but MacKeith continued the research, which resulted in the only study published regarding paracosms.
Together, Silvey and MacKeith established four criteria for paracosms: the subject must understand the paracosm to be imaginative, not real; the subjects paracosm must show longevity, typically a year or more; the subjects paracosm must be consistent throughout, with no dramatic changes; and the subject must demonstrate pride in and enjoyment of the paracosm, rather than use it as a defensive "escape" mechanism. The completed project resulted in a book chapter in 1988 (Morrison, Organizing Early Experience). Psychologist David Cohen joined with MacKeith to further analyze the information, which resulted in a more extensive summary, The Development of Imagination: The Private Worlds of Childhood. Cohen has further explored the world of paracosms in his book The Development of Play, in which he notes that Piaget mentions a nephew who had developed an intricate world, meticulously researched and documented.
I had several of these as a child. The most elaborate was a small nation that my sister and I dreamed up, populated entirely by talking animals (represented by our stuffed animals, natch). The Zoocratic Republic of Zoia had its own language, history, system of government, yearly elections, national anthem, monetary system, a big beautiful map, and a monthly news magazine which we put together on our father's Xerox machine. We must have kept it going for a period of two to three years. This article claims that paracosms are rather rare, but I can't imagine that we were the only children doing this. Anyone?