Female serial killers are rare compared to their male counterparts. Sources suggest that female serial killers represented less than one in every six known serial murderers in the United States between 1800 and 2004 (64 females from a total of 416 known offenders), or that around 15% of U.S. serial killers have been women, with a collective number of victims between 427 and 612. The authors of "Lethal Ladies", Amanda L. Farrell, Robert D. Keppel, and Victoria B. Titterington, state that "the Justice Department indicated 36 female serial killers have been active over the course of the last century." According to "The Journal of Forensic Psychiatry & Psychology", there is evidence that 16% of all serial killers are women.