title: The Quality of Life Questionnaire Core 30 (QLQ-C30) and Functional Assessment of Cancer-General (FACT-G) differ in responsiveness, relative efficiency, and therefore required sample size.
abstract: OBJECTIVE
  Quality of Life Questionnaire Core 30 (QLQ-C30) and Functional Assessment of Cancer Therapy-General (FACT-G) are widely used cancer-specific health-related quality of life (HRQOL) questionnaires. We aimed to compare their responsiveness with clinically important effects and statistical efficiency to detect such effects.
  
  
  METHODS
  Secondary analysis of QLQ-C30 and FACT-G data from a randomized controlled trial of Medical Qigong (n = 162 heterogeneous cancer patients). Difference in responsiveness (DR) and relative efficiency (RE) were calculated for five domains.
  
  
  RESULTS
  FACT-G total score was more efficient than QLQ-C30 global scale for detecting change within the intervention arm [RE = 0.31 (0.083, 0.69)] and comparing change between trial arms [RE = 0.17 (0.009, 0.58)]. In the social domain, the QLQ-C30 scale was more responsive [DR = 0.28 (0.024, 0.54)] and more efficient within arm only [RE = 5.25 (1.21, 232.26)]. In the physical, functional/role, and emotional domains, neither questionnaire was more responsive or efficient.
  
  
  CONCLUSIONS
  FACT-G would require about one-third the sample of QLQ-C30 to detect a given change in overall HRQOL, whereas in the social domain, it would require five times the sample size. FACT-G won advantage in overall HRQOL by reduced "noise" (smaller standard deviation achieved by summing across 27 items), whereas QLQ-C30 won advantage in the social domain via a larger "signal" (achieved through well-targeted item content).
authors.affiliation: Psycho-oncology Co-operative Research Group (PoCoG), School of Psychology, University of Sydney, New South Wales, Australia 2006. Electronic address: madeleine.king@sydney.edu.au.
authors.forename: Madeleine T
authors.initials: MT
authors.lastname: King
authors.forename: Melanie L
authors.initials: ML
authors.lastname: Bell
authors.forename: Daniel
authors.initials: D
authors.lastname: Costa
authors.forename: Phyllis
authors.initials: P
authors.lastname: Butow
authors.forename: Byeongsang
authors.initials: B
authors.lastname: Oh
mesh_terms: D000203:Activities of Daily Living; D006801:Humans; D009369:Neoplasms / Q000628:therapy*; D011788:Quality of Life; D015203:Reproducibility of Results; D018401:Sample Size; D011795:Surveys and Questionnaires; D016896:Treatment Outcome
keywords: Health status; Quality of life; Reliability; Sample size; Statistical data analysis; Validity