Development and Validation of a Physical Performance Instrument for the Functionally Impaired Elderly: The Physical Disability Index (PDI)

Abstract

Article describes development of the Physical Disability Index (PDI), an observer-administered, performance-based instrument measuring physical disability in frail-elderly persons without severe cognitive impairment. Sixty-five items in four subscales encompassing Range of Motion (ROM), Strength (STR), Balance (BAL), and Mobility (MOB) were measured. Subjects were randomly selected frail nursing home residents (N = 103) with a Folstein Mini-Mental State Exam (MMSE) score of ≥ 11. Using correlation matrices, cluster analysis, and regression techniques, the scale was reduced to 54 items. All individual item values were standardized and aggregated into subscale and summary PDI scores, each with a range of 0–100. Test-retest and interrater reliability were evaluated. Discriminant and convergent validity were established using MMSE, Physical Self-Maintenance Scale (PSMS), and Sickness Impact Profile–Physical Dimension (SIP-PD). PDI is a performance-based instrument that appears to discriminate among frail individuals with differing levels of physical function. Further testing is warranted in other populations of frail-elderly persons to ascertain its applicability and generalizability.