Primary care functioning scale showed validity and reliability in patients with chronic conditions: A psychometric study

Objectives: We evaluated the psychometric properties of a newly developed self-report questionnaire that aims for a more person-centered approach in primary care for patients with chronic conditions, the Primary Care Functioning Scale (PCFS). Study Design and Setting: To test the measurement properties of the PCFS, we asked patients with diabetes, cardiovascular disease, and chronic pulmonary disease to complete the PCFS questionnaire. The PCFS is entirely based on the International Classification of Functioning, Disability, and Health (ICF), consisting of 52 ICF-related items covering body functions, activities and participation, environmental factors, and personal factors. We analyzed three hypotheses representing different item sets of the 34 ICF-related items that assess the level of functioning (body functions, activities, and participation). We tested for unidimensionality, differential item functioning, reliability, and criterion-related validity. Results: Five hundred and eighty-two patients completed the questionnaire. The total scores of the polytomous and dichotomized items from the overall set 'body functions, activities and participation' demonstrated unidimensionality, good reliability (>0.80), and stability over time without bias from background variables. Conclusion: In sum, the PCFS can be used as a valid and reliable instrument to measure functioning in patients with chronic morbidity in primary care