Rationale: Disability and loss of function are acknowledged as important problems for people living with chronic obstructive pulmonary disease (COPD), but there is a need for validated tools to assess them. Objectives: The Late-Life Function and Disability Instrument (LLFDI) was originally validated for community-dwelling older adults. The full instrument has not been validated to assess disability and loss of function in people with COPD. Methods: People with COPD from six European countries completed the LLFDI as part of an observational study. Its validity was assessed in terms of 1 ) levels and distribution of LLFDI domain and subdomain scores; 2 ) floor and ceiling effects; 3 ) instrument structure (three domains, seven subdomains) by confirmatory factor analysis; and 4 ) construct validity by convergent validity, which is based on Spearman correlation with COPD-relevant and related constructs (functional exercise capacity, severity of dyspnea, and COPD-related health status), and known-groups validity, which is based on the distribution LLFDI scores according to COPD-meaningful groups (disease severity, age groups, and use of a walking aid). Results: The study included 605 participants (ages 68 +/- 8 yr, 37% female; FEV1= 54 +/- 20 % predicted). Most had impaired disability and function levels. We observed no floor effects and a ceiling effect in only two subdomains. Confirmatory factor analysis showed a moderate model fit for all LLFDI domains. Most of the correlations met our hypotheses (73%), with moderate to strong correlations for the function domain ( r min-max = 0.25-0.70), followed by the disability limitation domain ( r min-max = 0.15-0.54), and weakest correlations in the disability frequency domain ( r min-max = 0.04-0.41). The disability limitation and function domains differed by disease severity, age group, and use of a walking aid. The disability frequency domain differed by disease severity and use of a walking aid, but not by age groups. Conclusions: The LLFDI, a valid patient-reported outcome to investigate disability and function, has proven good construct validity in people with COPD. Clinical trial registered with the ISRCTN registry (ISRCTN no. 12051706); https://www.isrctn.com/ISRCTN12051706.
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