title: Variability and sample size requirements of quality-of-life measures: a randomized study of three major questionnaires.
abstract: OBJECTIVE
  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).
  
  
  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 the FLIC had a larger effect size in a cross-sectional and longitudinal setting, respectively, than the EORTC QLQ-C30 in differentiating patients with different performance status (both P < .05).
  
  
  CONCLUSIONS
  In some aspects, the FACT-G and FLIC global QOL scores had smaller variability and larger discriminative ability than the EORTC QLQ-C30. Further research using other criteria to compare the three instruments is recommended.
authors.affiliation: Division of Clinical Trials and Epidemiological Sciences, National Cancer Centre, Singapore 169610. cheungyb@graduate.hku.hk
authors.forename: Yin-Bun
authors.initials: YB
authors.lastname: Cheung
authors.forename: Cynthia
authors.initials: C
authors.lastname: Goh
authors.forename: Julian
authors.initials: J
authors.lastname: Thumboo
authors.forename: Kei-Siong
authors.initials: KS
authors.lastname: Khoo
authors.forename: Joseph
authors.initials: J
authors.lastname: Wee
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000150:complications / Q000523:psychology*; D011788:Quality of Life; D015203:Reproducibility of Results; D018401:Sample Size; D011795:Surveys and Questionnaires