external variables. RA scores correlated higher than PA scores on self-report measures of irritability and anger control. PA scores, by comparison, correlated more highly with measures of antisocial/impulsive behavior, extraversion, neuroticism, self-harm, and overall aggression—a profile that is consistent with the finding that antisocial and psychopathic individuals are prone to PA (Stanford et al., 2003). Subsequently, the two factors identified in the original study were validated using the IPAS in forensic patients (Kockler, Stanford, Nelson, Meloy, & Stanford, 2006), conduct disordered adolescents (Mathias et al., 2007), and college students (Haden, Scarpa, & Stanford, in press). In these studies, the correlation between the two scales was low, ranging from r=−.02 to .32, demonstrating that the independence of the scales, and the internal consistency of the scales, was acceptable (α ≥.72). Haden et al. (in press) also demonstrated a strong relation between RA and anger as well as negative life events. A psychometric study of the IPAS with methadone maintenance patients (Conner, Houston, Sworts, & Meldrum, 2007b) showed that the scales had a low intercorrelation (r= .02), acceptable internal consistency (α ≥.74), and good test-retest reliability (intraclass correlation ≥ .63), supporting their use with treated substance abusers.
