Objective: To evaluate psychometric performance of the NCCN-FACT Ovarian Cancer Symptom Index-18 (NFOSI-18) in advanced ovarian cancer. Methods: Cross-sectional, observational data from patients receiving treatment for ovarian cancer. Other measures included European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire core (EORTC QLQ-C30) and associated ovarian cancer module (EORTC QLQ-OV28) and Work Productivity and Activity Impairment. Internal consistency reliability, construct validity and anchor-based clinically important differences were assessed. Results: 897 patients were analyzed. Reliability was acceptable for all NFOSI-18 scores; construct validity was supported. Twelve anchors sufficiently correlated with NFOSI-18 scores and suggested clinically important differences: NFOSI-18 total score (5-7), disease-related symptoms - physical (3-4), disease-related symptoms - emotional (1), treatment side effects (2) and functional well-being (1-2). Conclusions: Results provide evidence of reliability and validity of NFOSI-18 scores. Generated CIDs will help improve interpretation of between-group treatment differences in clinical trials.
Keywords: NFOSI-18; clinically important difference; interpretation; ovarian cancer; patient-reported outcomes; psychometric properties.
Lay abstract The National Comprehensive Cancer Network Functional Assessment of Cancer Therapy – Ovarian Cancer Symptom Index-18 (NFOSI-18) is a questionnaire assessing the health of patients with ovarian cancer. When using such questionnaires, it is important to evidence that they produce consistent scores (referred to as reliability) and are aligned with other assessments of health (referred to as construct validity). It is also important to set guidelines on what constitutes a clinically important difference in scores, so clinicians and researchers can judge how effective new treatments are. This study analyzed data from 897 patients with advanced ovarian cancer, providing evidence of reliability and construct validity. Guidelines for clinically important differences were also provided. The findings support continued use of the NFOSI-18.