Stevenson founded the unit at the University of Virginia that investigates young children who make statements about a life they say they lived before, and he spent forty years building a catalogue of more than two thousand such cases. The method he described is documentary rather than experimental. A child, usually between two and five, speaks about another family, another place, a name, a manner of death. The investigator records those statements, ideally before the two families have met, then goes to the named place and checks whether a person answering the description existed and died in the way described. Where the child carries a birthmark or a malformation, he sought medical or postmortem records of the corresponding wound.
Two features of the collection are not in dispute and are worth stating. The cases cluster heavily in places where rebirth is an ordinary belief, in South Asia, Southeast Asia, Lebanon, Turkey and among certain groups in North America, which either reflects where such reports are taken seriously enough to be made or reflects what the belief itself produces. And the number of statements recorded in writing before any contact between the families is small, a point Stevenson himself made repeatedly, because by the time an investigator hears of a case the families have usually already found each other.