The Macdonald triad (also known as the triad of sociopathy or the homicidal triad) is a set of three behavioral characteristics that has been suggested, if all three or any combination of two, are present together, to be predictive of or associated with later violent tendencies, particularly with relation to serial offenses. The triad was first proposed by psychiatrist J.M. Macdonald in "The Threat to Kill", a 1963 paper in the American Journal of Psychiatry. Small-scale studies conducted by psychiatrists Daniel Hellman and Nathan Blackman, and then FBI agents John E. Douglas and Robert K. Ressler along with Dr. Ann Burgess, claimed substantial evidence for the association of these childhood patterns with later predatory behavior. Although it remains an influential and widely taught theory, subsequent research has generally not validated this line of thinking.