Psychometric properties of scale constructed from the International Classification of Functioning, Disability and Health (ICF) core set for breast cancer based on Rasch analysis.

ABSTRACT

OBJECTIVES: The purpose of this study was to construct a clinical instrument to measure functioning in breast cancer survivors using the International Classification of Functioning, Disability and Health (ICF) categories for body functions, activity and participation, and environmental factors, based on a Rasch analysis. METHODS: Items were generated from the brief ICF core set for breast cancer and in-depth interviews from eight oncologists. Psychometric properties were evaluated in 158 female Korean patients with breast cancer using Rasch analysis, such as fit of the ICF categories, targeting between the ICF categories and a person's abilities, unidimensionality, and reliability. RESULTS: The Rasch refinement led to a change from the original 43-item, 5-level scale to a 30-item, 3- or 4-level scale. Rasch reliabilities were 0.89 (body function scale), 0.96 (activity and participation scale), and 0.93 (environmental scale). The item-difficulty hierarchy was stable across age (<50 or ≥50 years) and had no non-fitting items or gaps (all information weighted fit (infit)/outlier sensitive fit (outfit) mean square error of 0.7-1.3, n = 140). CONCLUSION: The Brief Core Set Breast Cancer Questionnaire for Screening is a reliable and valid 30-item questionnaire based on the brief ICF core set. It allows measurement of functioning as a unidimensional construct in patients with breast cancer.