of death (based on a subset of 68 victims for whom the specific age at time of death was listed in the file information) was 31.6 years (SD ” 9.5; range ” 3–92). The general age group of the victim was reported in 100 cases. Eight victims were children (0–12 years old; 8%), 15 were teenagers (15%), 69 were adults (20–64 years old; 69%), and 8 were seniors (65 years and older; 8%). In addition, in 8 cases (6.4%) the offender had more than one victim during his current homicide offense.
Relationship Between Psychopathy and Homicide Offense
Instrumental/reactive differences as a function of psychopathy. Overall, 45 (36%) homicides were purely instrumental, 25 (20%) were instrumental/reactive, 29 (23.2%) were reactive/instrumen- tal, 16 (12.8%) were purely reactive, and 10 (8%) could not be coded. Possible differences in the violence committed by the psychopathic and nonpsychopathic groups were examined.2 Re- sults indicated that there was a significant difference between the two groups, t(113) ” 3.73, p # .001, “2 ” .11.3 Specifically, homicides perpetrated by psychopaths were associated with a higher degree of instrumentality (M ” 3.47, SD ” .82) than homicides committed by nonpsychopaths (M ” 2.65, SD ” 1.10). There also was a significant correlation between the continuous PCL–R total scores (0–40) and the instrumental ratings. Higher scores on the PCL–R were associated with higher levels of instru- mental violence, r(115) ” .45, p # .001.4 Psychopaths and non-
psychopaths were then compared on whether their violence was primarily reactive (rating of 1–2) or primarily instrumental (rating of 3–4). Results indicated that, overall, 70 (60.9%) of the offend- ers had committed a primarily instrumental homicide, whereas 45 (39.1%) offenders had committed a primarily reactive homicide. Again, a significant relationship between type of homicide and psychopathy was found. Specifically, psychopathic offenders were far more likely, #2(1, N ” 115) ” 17.96, p # .001, to have used primarily instrumental violence (93.3%), compared with nonpsy- chopathic offenders who were more likely to have committed primarily reactive rather than instrumental violence (51.6%; (see Figure 1). It is interesting that nonpsychopathic offenders (48.4%) also were clearly capable of committing primarily instrumental homicides but to a much lesser extent than psychopaths.
An analysis of the three separate dimensions (affect, instrumen- tal gain, and impulsivity) revealed that although these dimensions were partially interrelated, they each contributed in a meaningful way to the instrumental/reactive coding scheme. As expected, gain ratings were significantly negatively correlated with impulsivity ratings, r(109) ” $.62, p # .001, and negatively (nonsignifi- cantly) correlated with ratings of affective arousal, r(48) ” $.26, p ” .078, whereas affect and impulsivity were positively corre- lated, r(50) ” .59, p # .001. Further, as expected, gain ratings were significantly positively related to the instrumental/reactive ratings, r(112) ” .63, p # .001, whereas affect, r(50) ” $.54, p # .001, and impulsivity, r(112) ” $.84, p # .001, were significantly negatively related.
A hierarchical regression analysis was conducted with affect, gain and impulsivity entered sequentially as potential predictors of the instrumental/reactive ratings. The model was significant, adjR2 ” .70, F(3, 44) ” 37.36, p # .001. Specifically, when affect was entered into the model, it significantly predicted instrumental/ reactive ratings, chR2 ” .27, F(1, 46) ” 16.87, p # .001. Next, the gain dimension was entered and was also found to add signifi-
1 Although kappa is most commonly used when comparing the reliabil- ity of dichotomous variables, its suitability for a multileveled categorical variable has also been shown to be appropriate (Carletta, 1995; Howell, 1992).
2 As mentioned in the introduction, from our theoretical framework we conceptualized the ratings as representing a continuum. We also analyzed the instrumental/reactive data categorically using a nonparametric ap- proach and obtained the same pattern of results.
3 When the 29 PCL–Rs that had been completed by the researchers (on the basis of file information only) were excluded from this analysis, the effect size was almost identical (p # .001, “2 ” .12), indicating the same pattern of results as obtained with the full sample.
4 Previous literature has suggested that individuals who score above 20 on the PCL–R also display many of the characteristics of psychopathy, although they are not formally labeled as psychopathic. Therefore, the sample also was broken down into three PCL–R categories of low (0–20; n ” 39), medium (20–30; n ” 46), and high (30–40; n ” 30) psychopathy. Similar significant results were again obtained, F(2, 112) ” 16.32, p # .001. Specifically, the high-psychopathy group (M ” 3.47/4) committed 60% instrumental, 33.3% instrumental/reactive, 0% reactive/instrumental, and 6.7% reactive homicides. The medium-psychopathy group (M ” 3.04/4) committed 43.5% instrumental, 23.9% instrumental/reactive, 26.1% reactive/instrumental, and 6.5 % reactive homicides. The low-psychopathy group (M ” 2.18/4) committed 17.9% instrumental, 10.3% instrumental/ reactive, 43.6% reactive/instrumental, and 28.2% reactive homicides.
440 WOODWORTH AND PORTER