Psychometric Properties of the Functional Performance Inventory in Patients With Chronic Obstructive Pulmonary Disease

BACKGROUND: The Functional Performance Inventory (FPI) is a subjective measure of the performance dimension of functional status, based on an explicit analytical framework and the experiences of patients themselves. OBJECTIVES: To describe the conceptual foundation of the instrument, the procedures used to maximize content validity, and the results of the initial psychometric testing of the FPI in patients with chronic obstructive pulmonary disease (COPD). METHOD: Items and response structure for the instrument were drawn from the literature and qualitative interviews with 12 men and women with COPD. Twenty-four clinical and scientific experts participated in content validation. To assess the FPI's psychometric characteristics, 154 patients participated in a cross-sectional mail survey; 54 took part in a 2-week reproducibility assessment. Forty relatives were also included in validity testing. RESULTS: The instrument was internally consistent (alpha = .96) and reproducible (ICC = .85). Validity was evident in the significant (p < .001) correlations found between the FPI total score and the Functional Status Questionnaire (activities of daily living, r = .68; instrumental activities of daily living, r = .68), Duke Activity Status Index (r = .61), Bronchitis-Emphysema Symptom Checklist (r = -.59), Basic Need Satisfaction Inventory (r = .61), and Cantril's Ladder of Life Satisfaction (r = .63). The relationship between patient FPI score and relative perception of functioning, using the Katz Adjustment Scale for Relatives, was also significant (socially expected activities, r = .53; free-time activities, r = .49, p < .01). The instrument discriminated between patients with severe and moderate levels of perceived severity and activity limitation (t = 8.52, p <.001) and patients with FEV1 greater than and less than 1.0 liter (t = 4.25, p < .001). CONCLUSIONS: Results suggest that the FPI is a useful measure of functional performance in patients with COPD. Further development of the spiritual activities and work and school domains is in order, as is additional study of the instrument's responsiveness to change.