7. PROJECT SUMMARY/ABSTRACT Developmental disabilities (DD), including autism spectrum disorder (ASD), Down syndrome, Fragile X syndrome, and other intellectual and developmental disabilities are heterogeneous neurodevelopmental disorders that place considerable burden on individuals, families, and society. Although most research on DD has focused on children, these conditions are life-long with few established treatments to support functioning in adulthood. As a result, many adults with DD experience significant functional impairment represented by low rates of employment, severe social dysfunction and isolation, and a limited ability to live independently and experience autonomy in adult life. The development of interventions to improve adult functional outcomes in social, employment, and independent living domains across DD has lagged far behind those developed for children. A key factor limiting the development of treatments to improve adult functioning in DD is the lack of validated assessments of functional outcome applicable to adulthood. Current studies either use measures relevant to childhood with limited applicability to and treatment sensitivity in adults, or fail to assess this important domain, greatly restricting knowledge on how adult functioning can be improved in DD. We have shown in preliminary studies with adults with ASD that it is possible to develop measures of functional outcome in adulthood that have greater validity and are more sensitive to treatment effects than existing measures adapted from childhood. In response to this major gap in adult outcome measurement in DD and PAR-18-039, “Outcome Measures for Use in Treatment Trials of Individuals with Intellectual and Developmental Disabilities”, this project proposes to use NIH PROMIS methods to develop and validate proxy- and self-report versions of the Adult Functioning Scale (AFS) for assessing functional outcomes in social, employment, and independent living domains in adults with DD. A pool of potential items will be generated based on our conceptual model, functional outcome measures used in other populations, and input from expert and stakeholder panels. This item pool will then be completed by two calibration samples: Proxy reporters (e.g., parents, clinicians, group home staff) for 1000 adults with DD representative of the full range of verbal and intellectual functioning in DD and 1000 self-reporting adults with DD (N = 500 with ASD, N = 500 with other DD). Advanced psychometric analytics employing exploratory and confirmatory factor analysis and item response theory models will be used to create final calibrated item banks (and static short forms) of the AFS suitable for broad use in clinical trials across heterogeneous DD. The reliability and validity of the AFS caregiver and self-report versions will be examined in the calibration samples, along with a 4-week retest subsample (N = 200). Sensitivity to treatment- related changes will be assessed in longitudina...