Psychiatrist Ian Stevenson, from the University of Virginia, conducted more than 2,500 case studies over a period of 40 years and published twelve books. He wrote that childhood memories ostensibly related to reincarnation normally occurred between the ages of three and seven years then fade shortly afterwards. He compared the memories with reports of people known to the deceased, attempting to do so before any contact between the child and the deceased's family had occurred, and searched for disconfirming evidence that could provide alternative explanations for the reports aside from reincarnation.