Psychometric Evaluation of the Dutch Version of the Impulsive/Premeditated Aggression Scale (IPAS) in Male and Female Prisoners

Aggressive behavior is traditionally classified into two subtypes, impulsive and premeditated aggression. The Impulsive/Premeditated Aggression Scale (IPAS) is a self-report questionnaire to measure a person's tendency towards these subtypes of aggressive behavior. This study reports on the psychometric quality of the Dutch translation of the IPAS in a sample of 149 male and 70 female prisoners in the Netherlands. Confirmatory Factor Analysis yielded two factors with an item composition quite similar to those found in previous studies: impulsive aggression, 17 items; premeditated aggression, 13 items. For both factors reliable subscales could be composed for males and females: impulsive aggression alpha(males) = .92, alpha(females) = .94; premeditated aggression alpha(males) = .90 and alpha(females) = .91. The subscales were highly correlated: r(males) = .70, r(females) = .75. It is concluded that the underlying structure of the Dutch version of the IPAS is similar to the original version of the questionnaire, that internal consistency of the two subscales is good, and that the correlation between the two subscales is higher than previously reported. Possible reasons for the high correlation of the subscales are discussed. Additional studies are needed to establish the construct and criterion/predictive validity of the IPAS in the forensic field