Reliability of the assessment of dual diagnosis (ADD).

Emotional and behavioral problems are a major source of additional handicap for children, adolescents, and adults with mental retardation. To address these problems, clinicians need psychometrically sound instruments for assessing psychopathology in individuals with mental retardation. The initial psychometric properties of the Assessment for Dual Diagnosis (ADD), a new scale designed to screen for psychopathology in individuals with mild and moderate mental retardation, was examined. The authors conducted a preliminary evaluation of the interrater and test-retest reliability of the ADD. It was determined that the ADD had high stability across raters and high stability over time. In addition, good internal consistency was established with coefficient alpha. Potential uses for the scale and directions for future research are discussed.