There is a need to identify the most appropriate standardized instruments for research evaluating pharmacotherapy for youth with violent and aggressive behaviors. Youth violence and aggression are heterogeneous behaviors which differ depending on age and gender.

Instruments used in randomised controlled trials evaluating efficacy of pharmacotherapy in conduct disorder and its comorbidities were reviewed for psychometric, administrative and practicality evidence. Evidence was rated on a 3-point scale, adapted from the Scientific Advisory Committee's Instrument Review Criteria.

Of the nine included instruments, the Nisonger Child Behavior Rating Form (NCBRF), Conners' 3rd Edition, and Behavior Problems Inventory (BPI-01) were rated the highest for their psychometric properties. The Children's Aggression Scale (CAS), Aberrant Behavior Checklist (ABC) and Disruptive Behavior Disorder Rating Scale (DBDRS) were rated moderate, and the Child Behavior Checklist (CBCL), Modified Overt Aggression Scale (MOAS) and Swanson, Nolan, and Pelham Rating Scale (SNAP-IV) were rated lowest. The NCBRF, BPI-01 and CAS were the only instruments that could be used to measure both frequency and severity of aggressive behaviors. The CAS and MOAS featured the most items pertaining to violence and aggression.

The broad-band scales, the NCBRF and Conners' 3rd Edition, rated highest for their psychometric properties, however their usefulness in youth violence and aggression research is limited. The heterogeneity of aggressive and violent behaviors, age, gender, functional level, situational context and the type of informant should be taken into account when considering an appropriate instrument. All items in the CAS and the MOAS can be used to measure violent and/or aggressive behaviors. Further research into the psychometric properties of the MOAS in violent and aggressive youth is required before its use can be recommended. The CAS was found to be the most psychometrically sound and useful instrument that exclusively measures aggressive behaviors in youth.