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Should you be more afraid of the impulsive or the premeditated murderer?

Monday, August 5, 2013
posted by Douglas Keene

Dexter murdererNo, this isn’t one of those conversation starters for dinner table conversation although you can feel free to use it as such. Actually, it would likely go better with after dinner drinks. It’s a bit too daunting for dinner.

It’s long been advised (at least in forensic psychology circles) that when it comes to staying alive, you really want to steer clear of any psychopath with a low IQ who is abusing drugs and/or alcohol. It just isn’t going to end well. That was more common wisdom though (provided to those who wondered what the best policy was when dealing with unintelligent, drunk psychopaths) and now (ta-da!) we have actual research to prove it.

Researchers at Northwestern, DePaul and the University of Illinois at Chicago examined 77 inmates (90% male, 68% African-American, average age of 32 with a range of 16 to 67 years, and an average of 10.5 years of education) who were incarcerated in Illinois and Missouri. They sorted these inmates (who had either been charged with or convicted of the murders of 137 different people) into two groups: the affective/impulsive group and the premeditated/predatory group using Meloy’s forensic criteria (included in the article’s Appendix) related to psychopathy. The authors further define the group assignment as follows:

Predatory/Instrumental violence is “a planned, purposeful, and primarily cognitively derived act, whereas Affective/Impulsive violence refers to reactive, immediate, and primarily emotionally derived acts”.

Every inmate tested had been referred by their attorney or by the court for neuropsychological evaluation related to fitness to stand trial, criminal responsibility, mental retardation or neuropsychological abnormalities. The referrals were made across all phases of trial and all evaluations were completed between 2000 and 2007. Only one inmate was eventually found to be NGRI (not guilty by reason of insanity) by the court. The researchers were interested in examining the neuropsychological and intelligence differences, if any, between these two groups of both accused and convicted Defendants. All inmates participated in a clinical interview and completed a neuropsychological test battery. (For those interested in such things, the test battery included the Wechsler IQ test [WAIS-III]; subtests of the Wechsler Memory Scale, Third Edition; California Verbal Learning Test, Second Edition; Wisconsin Card Sorting Test, Conners’ Continuous Performance Task II, the Trail Making Test, the Stroop Color and Word Test, and the Controlled Oral Word Association Test. In short, they took a lot of tests.)

Here is what the researchers found upon comparing the two groups:

Affective/Impulsive Defendants were younger, less educated, more likely to be African-American, more likely to have a history of substance abuse (93% to 76%) or developmental disorders and less likely to have a history of psychiatric diagnosis or personality disorder than were those Defendants in the Predatory/Instrumental group.

Affective/Impulsive Defendants had lower overall IQ scores (79, in the Borderline Range) while Predatory/Instrumental Defendants scored in the Average Range (93).

Affective/Impulsive Defendants had lower overall memory retention, lower scores on attention and task completion, and poorer face recognition.

Affective/Impulsive Defendants had lower problem-solving efficiency and cognitive flexibility.

Predatory/Instrumental Defendants were more likely to have both Axis I (major mental disorders such as Schizophrenia or Bipolar Disorder) and Axis II disorders (personality disorders such as Antisocial, Narcissistic, Histrionic, Borderline, and so on).

The researchers say what all this means is that Affective/Impulsive Defendants have “significant neuropsychological and intellectual deficits” while Predatory/Instrumental Defendants are “largely intact across neurocognitive domains”. In English, that means the Affective/Impulsive Defendants had multiple mental and developmental problems while the Predatory/Instrumental Defendants were “pretty much okay” when their intellectual and neurocognitive functions were assessed–but, of course, very much not okay on measures of what constitutes empathy for others.

So, planful murderers are most likely the predatory type, and the emotional/low intellect murderers tend to be the impulsive types. The former is likely to be smarter, and a bit less likely to be caught (or at least less quickly caught). The emotional/impulsive murderer is likely to commit the crime with less thought to the consequences, and without a plan for succeeding at it.

Our sage counsel is for you to stay away from both groups and away from psychopaths in general.

Hanlon, RE, Brook, M., Stratton, J., Jensen, M., & Rubin, LH (2013). Neuropsychological and intellectual differences between types of Defendants: Affective/Impulsive versus Predatory/Instrumental (Premeditated) Homicide. Criminal Justice and Behavior, 40


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