The development and psychometric evaluation of the Pulmonary Functional Status Scale: an instrument to assess functional status in pulmonary disease.
BACKGROUND: This article describes the development and psychometric evaluation of the Pulmonary Functional Status Scale (PFSS). The PFSS was developed to address the need for a self-administered, disease-specific, functional status outcome measure that was conceptually based, relatively short, and comprehensively assessed the psychosocial domains affected by chronic pulmonary disease. METHODS: Content validity of the PFSS was established by a panel of experts. Construct validity was determined by principal components factor analysis using data from 365 subjects derived from several studies that used the PFSS. The sample was predominantly white (80%), married (36%), and male (56%) with a mean age of 68.1 years, mean forced expiratory volume in one second of 1.18 L and mean forced vital capacity of 2.31 L. Test-retest reliability was evaluated in 17 outpatients with chronic obstructive pulmonary disease. Concurrent validity was assessed by correlating responses on the total PFSS with the Sickness Impact Profile (SIP) score (n = 39), and the 12-minute walk test (n = 104). RESULTS: The factor structure solution used 35 of the 50 submitted items, explained 48.7% of the variance, and yielded three factors: Daily Activities/Social Functioning, Psychological Functioning, and Sexual Functioning. Cronbach's alpha coefficients for the total PFSS was 0.93 and the test-retest correlation coefficient was rho = 0.75 (P = 0.001). The correlation between the total PFSS score and the SIP and 12-minute walk test were r = -0.54 (P < 0.001) and r = 0.62 (P < 0.001), respectively. CONCLUSION: The PFSS has solid psychometric properties that make it acceptable for use in clinical practice as well as research.