Variability and Sample Size Requirements of Quality-of-Life Measures: A Randomized Study of Three Major Questionnaires

Purpose To compare the variability and sample size requirements of the global quality-of-life (QOL) scores of the following three major QOL instruments: the Functional Assessment of Cancer Therapy–General (FACT-G), Functional Living Index–Cancer (FLIC), and European Organisation for Research and Treatment of Cancer Core Quality of Life Questionnaire C30 (EORTC QLQ-C30). Patients and Methods Cancer patients were randomly assigned to answer two of the three instruments using an incomplete block design (n = 1,268). The instruments were compared in terms of coefficient of variation, effect size in detecting a difference between patients with different performance status, and correlation coefficient between scores at baseline and follow-up. Results The FACT-G and FLIC had significantly smaller coefficients of variation than the EORTC QLQ-C30 (both P < .05). The FLIC also had significantly larger correlation coefficients between scores at baseline and follow-up than the EORTC QLQ-C30 (P < .05). The FACT-G and t...