Measurement Properties of the Patient-Specific Functional Scale in Individuals with Asthma

To analyse the reliability, construct and content validity, ceiling and floor effects, acceptability, and feasibility of the Patient-Specific Functional Scale (PSFS) in individuals with asthma. This methodological study included individuals with asthma. Sociodemographic and clinical characteristics, lung function (forced expiratory volume in one second - FEV1), asthma control, and quality of life (Asthma Quality of Life Questionnaire - AQLQ) were assessed, in addition to the administration of the PSFS. Reliability, construct, and content validity, as well as ceiling/floor effects, were analysed. One hundred participants were evaluated (88% women, mean age 56 ± 14 years), the mean PSFS score was 4.1 ± 2.3. Regarding reliability, the intraclass correlation coefficient was 0.95 (95% CI: 0.88-0.97, p < 0.0001). The PSFS showed a fair correlation with the AQLQ activity limitation domain (r = 0.34, p = 0.001) and a weak correlation with FEV1 (r = 0.16, p = 0.19). Lower scores were observed in participants with poorer asthma control (p = 0.03). 97% of the activities reported in the PSFS were classified under the activity and participation domain of the International Classification of Functioning, Disability, and Health (ICF). No ceiling or floor effects were detected. The PSFS demonstrated strong reliability, adequate validity, and no ceiling or floor effects, supporting its potential as a useful tool for assessing activity limitations in asthma.