What Is The MacDonald Triad—And What Does It Say About Serial Killers?

Wait, what is the Macdonald Triad?

In 1963, John Macdonald, then a professor of psychiatry at the University of Colorado School of Medicine and the associate director of inpatient service at the Colorado Psychopathic Hospital in Denver, came up with a theory that he, at the time, believed predicted future homicidality.

The theory originally featured five behaviors that were meant to be predictive of homicidal threats, according to Kori Ryan , PsyD, assistant professor of behavioral sciences at Fitchburg State University, who has studied the Macdonald Triad extensively. "Somehow along the way, two behaviors were dropped and his theory was applied to homicidality and violence, and eventually serial murder," she explains.

The three behaviors that remained-fire setting, bed wetting, and cruelty to animals-were deemed the Macdonald Triad.

Is the MacDonald Triad an accurate theory to determine serial killer behavior?

At first, the theory seemed to make sense. After all, some "widely cited" studies seemed to support the Macdonald Triad, but "the science was questionable," says Ryan. "The research on the Macdonald Triad almost became an academic game of 'telephone.'"

That's not surprising considering MacDonald originally developed his theory in an observational research paper of a small, homogenous group. Plus, according to Ryan, "a theory is developed with the intention of being disproven." She believes this has been done (more than once). There just isn't enough-or any, really-evidence to support the Macdonald triad as a definitive predictor of future homicidal behavior.

However, there is sufficient research to suggest that two of these behaviors-setting fires and cruelty to animals-are risk factors for a variety of issues, says Ryan. "But the [Macdonald] theory ignores a lot of individual, family, and systemic factors that we know to also be linked to these behaviors, such as abuse, poverty, psychopathology, developmental concerns."

Ryan adds, "I would hesitate to ever say there are definitive behaviors that would predict future violence." Instead, she says that certain behaviors are risk factors for a variety of potentially concerning outcomes.

Oh, and btw, John Macdonald agrees. According to Ryan, he later wrote a paper refuting his own theory, but that was largely ignored.

Okay, so why do people still think the Macdonald Triad indicates serial killer behavior?

Well, before the triad theory was pretty much debunked, it was already in popular culture, so many people were familiar with it, Ryan explains. That, combined with how easy it was to understand and apply in daily life, the nature of the topic, the incomplete or incorrect citing of the study, and just general faulty science "made the theory take on a life of its own," she says.

And you can still see the effect of the Macdonald triad today. Luckily, most of the information available with a quick Google search debunks the myth. Still, Ryan says, "My concern is that someone might hear about it in popular culture and take the triad as fact, rather than doing any additional research."

If you're still fascinated by serial killers (it's okay), see how the cast of 'Extremely Wicked' compare to their real-life counterparts:

What about the actual behaviors explained in the Macdonald Triad? Do they indicate anything?

Yes, but they're more "red flags," in Ryan's opinion, than anything else. If a child starts fires, wets their bed, and/or is cruel to animals, she recommends having them evaluated by a medical professional. "Not because they are necessarily predictive of violence or anything else," she clarifies. "But they are basically saying, 'I might need some additional help.'" That's it. It doesn't mean that child will automatically grow up to become a serial killer.

So, if your child or a child you know is exhibiting these behaviors, realize that there are tons of reasons why. "Sometimes, we can definitely say someone has a higher risk of violence as an adult because of many individual, familial, environmental, and systemic reasons," Ryan explains. "Others are exposed to, and have these risk factors, and never engage in any violence."

Ultimately, it's important to remember that "all behavior is on a spectrum," says Ryan. If youre concerned about your child's behavior, you may want to consider having a licensed mental health professional evaluate them. At the very least, Ryan says, that can help determine if your child needs some support or intervention.