Abstract
Measurement properties of patient-reported outcome measures assessing functional performance and activity limitations in interstitial lung disease (ILD) are often unknown. To evaluate the reliability and validity of the Canadian Occupational Performance Measure (COPM) and the Pulmonary Functional Status and Dyspnea Questionnaire-Modified version (PFSDQ-M) in European Portuguese among people with ILD, and to explore differences between fibrotic and non-fibrotic ILD. Cross-sectional study. Internal consistency (Cronbach's α), test-retest/intra-rater and inter-rater reliability assessed using intraclass correlation coefficients [ICC2,1[95%CI]], standard error of measurement (SEM), minimal detectable change at 95% confidence level (MDC95) and Bland-Altman analysis, and floor/ceiling effects were evaluated. Construct validity was explored with correlations: convergent validity with the LCADL, CIS-8, 6MWT and 1-minSTS, only for PFSDQ-M; divergent validity with age and lung function for both instruments. Subgroup analyses compared fibrotic and non-fibrotic ILD. A total of 334 participants were included. The COPM showed moderate test-retest/intra-rater and inter-rater reliability (ICC2,1 = 0.68[0.57-0.77]-0.72[0.63-0.80]), with SEM = 1.08-1.42 and MDC95 = 3.00-3.94, and no floor/ceiling effects. The PFSDQ-M demonstrated excellent internal consistency (α = 0.90-0.96) and good test-retest and inter-rater reliability (ICC2,1 = 0.80[0.74-0.85]-0.92[0.89-0.94]), with SEM = 15.80 and MDC95 = 43.80 for total score. Bland-Altman analysis showed no systematic bias for the COPM and a small bias for the PFSDQ-M test-retest. Moderate-to-strong correlations with LCADL/CIS-8 and weak-to-moderate with 6MWT/1-minSTS supported convergent validity for PFSDQ-M. Negligible-to-weak correlations with age and lung function for COPM and PFSDQ-M supported divergent validity. Subgroup results were similar. The European Portuguese COPM and PFSDQ-M demonstrated reliability. The COPM showed evidence of divergent validity, whereas the PFSDQ-M demonstrated both convergent and divergent validity. These findings support their use for assessing functional performance in people with ILD.