Impulsive/Premeditated Aggression Scale (IPAS)

The IPAS is a 30-item self-report instrument designed to characterize aggressive behavior as predominately impulsive or predominately premeditated in nature. Items are scored on a 5-point Likert-type scale (Strongly Disagree, Disagree, Neutral, Agree and Strongly Agree) and 20 items are scored to yield two subscale scores: IA and PM. The IPAS has been validated for juveniles, and its reliability estimates range from 0.72 to 0.82 (Stanford et al., 2003; Kockler et al., 2006; Mathias et al., 2007). The categorical scoring technique was used to classify participants into impulsive and premeditated groups. Items for which the individual answers Strongly Agree or Agree were rated as positive. The total number of positive items was determined for both the IA and PM scales. Then the percentage of positive items for IA and PM scales were calculated respectively. Difference between IA and PM percentage (P_d) was used to classify participants into predominately impulsive or predominately premeditated subtypes of aggression. Inmates with P_d in the lowest 25% were then excluded.