From QI-disability to QID-12: creating a brief proxy-report measure of quality of life for children with intellectual disability

Quality of Life Disability (QI-Disability) is a 32-item parent-report measure assessing quality of life (QOL) in children with intellectual disability across domains of physical health, positive emotions, negative emotions, social interactions, leisure and outdoors, and independence. This study aimed to develop and validate a short form for use in clinical and research settings. Caregivers of 1,699 children with intellectual disability aged 3–18 years and representing mild to profound functional impairments, completed the QI-Disability measure as part of different studies. A Genetic Algorithm (GA) was applied to select a reduced item set. The short form was evaluated against the original scale using correlational, reliability, and Rasch analyses. The GA-derived 12-item set (QID-12) represented each of the six QOL domains. Correlation between QID-12 and QI-Disability total scores was high (r = 0.97). Internal consistency of QID-12 was acceptable (α = 0.85). Rasch analysis demonstrated good fit of all items to the partial credit model, person separation reliability was 0.84, and there was no evidence of multidimensionality (p > 0.99). Item targeting was appropriate across the ability spectrum. Disordered category thresholds were observed for three items, but overall psychometric performance remained satisfactory. QID-12 provides a valid and reliable short form of the QI-Disability. It retains coverage of the key domains of child QOL while substantially reducing respondent burden, supporting its use in both clinical practice and population research. Measuring quality of life (QOL) in children with intellectual disability is typically based on parent or proxy-report. Existing QOL questionnaires are lengthy and may form part of a battery of measures that can be time consuming to complete. Thus, there is a need for briefer, psychometrically sound questionnaires that can reduce respondent burden and provide an overall measure of child QOL for some clinical or research contexts. The Quality of Life Inventory – Disability (QI-Disability) is a validated 32-item parent-report measure of children’s QOL across six domains - physical health, positive and negative emotions, social interaction, leisure and the outdoors, and independence. This study sought to develop and validate a short-form version of QI-Disability in a large sample of children with mild to profound intellectual disability. The resulting 12-item short-form (QID-12) demonstrated strong validity and reliability, capturing the six key domains of child QOL while substantially reducing respondent burden. These findings support the use of QID-12 in both clinical practice and population research taking into account that the short form is not intended to replace the full QI-Disability in all contexts.