Unheard Voices: A Systematic Literature Review of Studies Using Self-Report Methods to Gather the Perspectives of Autistic Adults with Intellectual Disability.

Background: Autistic individuals with intellectual disability remain significantly underrepresented in research, particularly in studies that capture their lived experiences through self-report methods. This systematic review critically examines existing research employing self-report methods in studies where the focus is on autistic adults who have intellectual disability, evaluating the scope of this research, the self-report measures used, and the extent of community involvement. Methods: We conducted a systematic literature review in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched PsycINFO, Scopus, MEDLINE, ERIC, CINAHL, and Web of Science for studies published between January 2013 and July 2023. We conducted a narrative synthesis to evaluate study characteristics, the use of self-report measures, and the involvement of autistic individuals and their communities in the research process. Results: Only 14 studies met the inclusion criteria. The majority focused narrowly on evaluating interventions, with little attention paid to exploring the broader lived experiences of autistic adults with intellectual disability. We identified 24 self-report measures, yet only two had been validated specifically for individuals with intellectual disability. Furthermore, less than half of the remaining measures reported the use of any adaptations or accommodations such as visual aids or simplified language. Alarmingly, community involvement was almost entirely absent, with no studies incorporating co-production with autistic individuals. Conclusions: This review reveals a critical and urgent need for autism research that genuinely includes and represents autistic adults with intellectual disability. It is imperative that future research prioritizes the development and rigorous validation of accessible self-report tools, expands its focus beyond intervention outcomes, and commits to the meaningful involvement of autistic individuals throughout the research process. Addressing these profound gaps is essential for building an equitable and inclusive body of knowledge that fully recognizes and responds to the diverse experiences within the autistic community. Community Brief: