When 12 seals were shot and mutilated on Ireland's north shores in 2009, a commentator quipped that the perp had to be some kid honing his serial killer skills.
Thanks largely to misconceptions and spotty research, the notion that the Macdonald triad (animal cruelty, fire-setting, and bed-wetting) points to murder-prone kids has become an entrenched stereotype. This easy formula carries a heavy load, but it actually offers little for the prediction of criminality.
How did it gain the status of fact?
In 1963, forensic psychiatrist J. M. Macdonald observed in a paper, "The Threat to Kill," that these behaviors (along with two others) often showed up in his most aggressive and sadistic patients. Macdonald had compared 48 psychotic patients against 52 non-psychotic patients who all had threatened to kill someone. (Note: The study was about those who had threatened a violent act, not committed one.) Just over half were male, and they ranged in age from 11 to 83.
Macdonald relied mostly on clinical observation to make his assessment and he did not believe the study had predictive value. In any event, his research group was small and unrepresentative.
Despite these glaring issues, other researchers decided that Macdonald's notion was worth testing.
A couple of years after Macdonald's publication, a team of psychiatrists divided 84 incarcerated offenders into two groups: nonaggressive (53) and aggressively violent (31). They found that three-fourths of the violent offenders showed evidence of one or two behaviors from the triad, and that 45% showed all three.
But their study, too, was small and poorly designed. When other researchers tried to replicate it with much larger groups and better controls, no one's results came close.
Nevertheless, some criminologists have applied the triad to various offender populations, including—and especially—serial killers. Although some violent offenders do have excessive fire-setting, animal cruelty, or bedwetting past age five in their backgrounds, rarely do all three behaviors show up. Other behaviors, such as callous disregard, occur more regularly.
In addition, some of the data on which claims are made about the triad's relationship to serial murder come from inaccurate true crime books or websites. Many authors today just assume that the Macdonald triad's predictive power has been roundly proven.
Among the most visible spokespeople on this relationship were former members of the FBI's Behavioral Analysis Unit. During the 1980s and 1990s, they offered evidence from their own studies, but their research, too, was flawed.
While on the road teaching local jurisdictions about behavioral analysis, several members of the then-Behavioral Science Unit interviewed offenders at nearby prisons. With no effort to work within a randomized scientific design, they gathered information from just 36 convicted murderers, only 25 of which were serial killers. All had voluntarily agreed to talk. Once more, the sample was too problematic to draw significant conclusions.
Yet several agents used this data to develop theories and publish articles. They found that nearly half of the subjects were from single-parent homes, three-fourths had described an indifferent or negligent parent, a majority had a psychiatric history, the mean IQ was bright normal, three-fourths had paraphilias, and the same percentage reported an experience of abuse.
In addition, although the agents found evidence in many of their subjects of at least one of the Macdonald triad factors, they supplied no data about the percentage that had all three. Enuresis, high on the list, was evident in more offenders than animal cruelty, and yet recent research has shown that enuresis is not an indicator of psychological maladjustment.
The data analysis from the BSU's study made its way into criminological texts as a reliable source, and only recently have researchers challenged it.
For a master's thesis, Kori Ryan submitted a study in 2009 that contradicts nearly half a century of claims. Ryan performed the most extensive review of the literature to date and found little empirical support for the triad's predictive value.
Together or alone, the triad behaviors can indicate a stressed child with poor coping mechanisms or a developmental disability; such a child needs guidance and attention. However, until we design and carry out better empirical studies than we've seen thus far, researchers and media agencies should refrain from stating that the triad identifies a future serial killer.