A tutorial on person ability scores for the IDD clinician

For clinicians working in intellectual and developmental disabilities (IDD), serial assessment of developmental constructs is crucial for understanding conditions that unfold over time and for informing medical and therapeutic decision-making. Standardized tests offer a range of score options, but the norm-referenced scores used to identify disability have serious limitations when used to track individual progress of individuals with IDD over time. Many tests produce Rasch analysis- or item response theory-based person ability scores, which are intended for use in the monitoring context. Although some allied disciplines such as education have used these scores for decades, ability scores are not commonly used by most clinicians working in IDD. Recent work has fleshed out the advantages of ability scores in research, but little attention has been paid to the clinical context. Here we provide an overview of the provenance of ability scores and their use in the IDD clinical context, including suggestions for the integration of ability scores in clinical practice.