Adult ADHD Self-Report Scale (ASRS-18): Validity evidence, a proposed factor structure, measurement invariance, and screening utility in Brazilian adults.

Attention-Deficit/Hyperactivity Disorder (ADHD) involves inattention and hyperactivity-impulsivity. The Adult ADHD Self-Report Scale (ASRS-18) is used for screening, but evidence in Brazilian adults remains limited. We examined the psychometric properties of the ASRS-18 in 805 Brazilian adults with and without a reported previous ADHD diagnosis. Results supported a two-factor structure (Inattention and Hyperactivity/Impulsivity) with acceptable CFI, TLI, and SRMR (CFI = .929; TLI = .919; SRMR = .060), and slightly above RMSEA (.085). Multigroup analyses supported configural, metric, and scalar invariance across adults with and without a reported previous ADHD diagnosis. Internal consistency was adequate (McDonald's omega .90 and .87). The scale discriminated between groups with and without a reported previous ADHD diagnosis, with large effects for Inattention (r = .56) and Hyperactivity/Impulsivity (r = .50). Receiver operating characteristic (ROC) analyses indicated discrimination of reported ADHD diagnosis status by total score (AUC = .83), Inattention factor (AUC = .83), and six-item Part A screener (AUC = .82). Positive predictive values fell under realistic base rates, so a positive result indicates further assessment; cutoffs were stable but remain preliminary and sample-specific. Significant correlations between ASRS-18 domains and measures of anxiety, depression, perceived stress, and impulsive buying supported validity based on relations with external variables. Findings provide evidence for validity and score reliability of the ASRS-18 in Brazilian adults.