Measurement of psychopathic personality traits
Psychopathic personality traits were assessed using the Psychopathic Personality Inventory. 19The PPI is a 187-item self-report questionnaire with a total score and 8 sub-scales designed to measure psychopathic personality traits in a dimensional manner.
- (a) Machiavellian egocentricity which is characterised by ‘looking out for one’s own interests before others’;
- (b) social potency, or the ‘ability to be charming and influence others’;
- (c) coldheartedness is the ‘propensity towards callousness, guiltlessness, and unsentimentality’;
- (d) carefree non-planfulness, is the ‘non-planning component of impulsivity’;
- (e) fearlessness, is the ‘absence of anxiety and harm concerning eagerness to take risks’;
- (f) blame externalisation, is the ‘tendency to view others as source of problems’;
- (g) impulsive non-conformity, is the ‘reckless lack of concern for social mores’;
- (h) stress immunity, is the ‘absence of marked reactions to otherwise anxiety provoking events’ (pp. 500–2). 19
Each item consists of a statement to which participants must indicate how accurately it applies to them using a 4-point scale ranging from 1 ‘false’ to 4 ‘true’. The PPI has been shown to have good convergent and discriminant validity in both community and criminal samples.19,23–27 In particular, it shows good criterion related validity when compared with structured, collaboratively rated clinical assessments of psychopathy such as the PCL–R. 18,24 The PPI scores for the sample are shown in Table 1. The mean total PPI score for the sample was lower than that reported by Lilienfeld et al (S. Lilienfeld, personal communication, 2008), for a large sample of substance misusing male prisoners (see online supplement for details). However, individuals in the present sample did show total scores at or above the criminal mean and the fearlessness, social potency, coldheartedness and stress immunity scores for the present sample were remarkably similar to those reported for the criminal population. Additional figures demonstrating the sample distribution of scores on each sub-scale can be found in the online Fig. DS1.
Table 1 The Psychopathic Personality Inventory scores for the sample