Attention deficit hyperactivity disorder (ADHD) in adults is increasingly recognized as a clinically important syndrome. The aim of this study was to evaluate the psychometric performance of a new scale for adult ADHD based on the widely used Symptom Checklist 90 Revised (SCL-90-R). Scale performance was assessed in a clinical study including 100 ADHD patients and 65 opiate-dependent patient controls, and in the Zurich study, an epidemiological age cohort followed over 30years of adult life. Assessments included a ROC analysis of sensitivity and specificity, internal consistency, test-retest reliability, external validity and measurement invariance over nine testing occasions. The new scale showed a sensitivity and specificity of 75 and 54%, respectively, internal consistency over 0.8 (McDonald's omega, Cronbach's alpha), one-year test-retest reliabilities over 0.7, statistically significant and substantial correlations with two other validated self-rating scales of adult ADHD (R=0.5 and 0.66, respectively), and an acceptable degree of longitudinal stability (i.e., measurement invariance). The proposed scale must be further evaluated, but these preliminary results indicate it could be a useful rating instrument for adult ADHD in situations where SCL-90-R data, but no specific ADHD assessment, are available, such as in retrospective data analysis or in prospective studies with limited methodical resource
