Reliability, validity and important difference estimates for the NCCN-FACT Ovarian Symptom Index-18 (NFOSI-18).

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.