Personalizing Functional Assessment in Chronic Obstructive Pulmonary Disease: A Validation Study of the Patient-Specific Functional Scale

<b>Background</b>: Personalized and accurate assessment of functional performance in chronic obstructive pulmonary disease (COPD) requires patient-centered tools that capture individualized activity limitations. The Patient-Specific Functional Scale (PSFS) is brief and clinically accessible, but its psychometric properties in COPD have not been fully established. This study aimed to evaluate the reliability and construct validity of the PSFS in individuals with COPD. <b>Methods</b>: A longitudinal psychometric evaluation was conducted with 70 adults diagnosed with COPD confirmed by spirometry. The PSFS was administered twice, 4-7 days apart, to examine test-retest reliability, standard error measurement (SEM), and minimal detectable change at 95% confidence interval (MDC_95%). Construct validity was assessed through correlations between the PSFS, the Duke Activity Status Index (DASI), and the St. George's Respiratory Questionnaire (SGRQ). Floor and ceiling effects were also evaluated. <b>Results</b>: Seventy participants (mean age 63 ± 11 years) completed the study. The PSFS demonstrated excellent test-retest reliability (ICC = 0.94; 95% CI: 0.90-0.96), and low SEM (0.16 points), and the MDC_95% was 0.44 points, with no floor or ceiling effects. Construct validity was supported by moderate positive correlations with DASI (r = 0.51, <i>p</i> < 0.001) and moderate negative correlations with SGRQ total scores (r = -0.41, <i>p</i> < 0.001). PSFS scores were not associated with demographic variables or COPD severity. <b>Conclusions</b>: The PSFS demonstrates strong psychometric properties in COPD, including excellent reliability and moderate construct validity. Its individualized approach, ease of administration, and ability to capture functional limitations beyond traditional clinical measures support its utility in both clinical practice and research for personalized functional assessment.