Measurement Properties of the Late Life Disability Index Among Individuals Who Use Power Wheelchairs as Their Primary Means of Mobility

Abstract

ObjectiveTo examine the reliability, validity, and factor structure of the Late Life Disability Instrument (LLDI) in individuals who use power wheelchairs as their primary means of mobility. DesignA 4-week, test-retest study design. SettingFive Canadian cities. ParticipantsThe validity sample included 115 new and experienced power mobility users, and the reliability sample included 85 experienced users (N=115). These volunteer samples included individuals who were aged ≥50 years and independently used power mobility as their primary means of mobility. InterventionsNot applicable. Main Outcome MeasureThe LLDI measures participation in 2 dimensions of 16 life activities: frequency and perceived limitations. Validity measures included the Wheelchair Skills Test–power version, the Assistive Technology Outcomes Profile for Mobility, the Hospital Anxiety and Depression Scale, the Power Mobility Wheelchair Confidence Measure, and the Life Space Assessment. ResultsFor the reliability sample, raw intraclass correlational coefficients for limitation and frequency dimension scores ranged from .855 (95% confidence interval .781–.905) to .883 (95% confidence interval, .822–.924), respectively. For the validity sample, scores on the LLDI were correlated as hypothesized with scores on validity measures. The factor structure that was identified with the original sample was not replicated among power wheelchair users. For LLDI frequency, exploratory factor analysis indicated that 5 of the original 16 items did not perform similarly among power wheelchair users. For LLDI limitations, a 1-factor, rather than a 2-factor, solution was identified. ConclusionsThe study provides evidence in support of the reliability and validity of the measure but suggests that the original subscale scores may not be applicable to power wheelchair users.