Measuring autonomy in disabled people: validation of a new scale in a UK population

Abstract

Objective: to evaluate the validity and reliability of an English version of the Impact on Participation and Autonomy Questionnaire (IPA). The original Dutch IPA has been shown to load onto five factors.Design: a validation study.Setting: outpatients clinics and people's homes.Subjects: two hundred and thirteen people with multiple sclerosis, rheumatoid arthritis, spinal cord injury, and general practice attendees, stratified by level of disability (median age 54, 42% male, 58% female). Inclusion criteria: English as first language, aged 18-75, Mental Status Questionnaire score > 6.Interventions: self- and interviewer-administered outcome measures.Main measures: IPA, including one new item (66 participants completed the IPA on a second occasion).Other measures: Short Form-36 Health Survey (SF-36), London Handicap Scale, three domains of the Functional Limitations Profile (FLP): household management, social integration, emotion.Results: confirmatory factor analysis confirmed the construct validity of the IPA (Normal Fit Index = 0.98, Comparative Fit Index = 0.99), indicating a good fit to the model. Convergent and discriminant validity were confirmed by the predicted associations, or lack of, with the exception of a poor association between the 'social life/relationships' IPA subscale and FLP-emotion. Internal reliability of the IPA was confirmed (Cronbach alphas > 0.8; item-total correlations for all subscales > 0.5). Test-retest reliability was confirmed for all items (weighted kappas > 0.6) and subscales (intraclass correlation coefficients > 0.90).Conclusions: the English IPA is a valid, reliable and acceptable measure of participation and autonomy in people with a range of conditions and can make a unique and fundamental contribution to outcome assessment. Further research is required to examine the responsiveness of the IPA to change over time, its clinical utility and suitability for use with people from ethnic minorities and with older people