title: Mapping the Gastrointestinal Quality of Life Index to short-form 6D utility scores.
abstract: OBJECTIVE
  The Gastrointestinal Quality of Life Index (GIQLI) is a disease-specific quality of life instrument that is commonly used in gastrointestinal disorders. However, no preference weights, which are used to calculate quality-adjusted life years for cost-effectiveness analyses, for this instrument have been assigned. Therefore, the objective of this study was to develop a mapping function to derive utility scores for the GIQLI.
  
  
  METHODS
  Patients undergoing elective laparoscopic cholecystectomy completed the short-form 6D (SF-6D), a preference-weighted utility measure, and the GIQLI at baseline and at 1 wk and 1 mo postoperatively. The responsiveness of the SF-6D to expected postoperative changes as well as the correlation between the SF-6D and the GIQLI was investigated. Ordinary least squares regression was performed to derive a mapping function using the baseline values, which was then validated using postoperative values. Adjusted r(2), mean absolute error, and root mean square error was used to determine model performance.
  
  
  RESULTS
  A total of 50 patients were included in the study (mean age 51.1 [standard deviation 16.8], 28% male). The SF-6D and GIQLI domains were responsive to expected postoperative changes, and there was high correlation between the SF-6D and four of the five GIQLI domains (excluding treatment effects). The final mapping function explained 63% of the variance in the derivation sample but had relatively high mean absolute error (0.075 and 0.067 in the 1-wk and 1-mo samples, respectively) and adjusted root mean square error (13.1% and 12.0% in the 1-wk and 1-mo samples, respectively).
  
  
  CONCLUSIONS
  The GIQLI can be accurately mapped to SF-6D preference weights at the group level but may be too inexact at the individual level.
authors.affiliation: Department of Surgery, Steinberg-Bernstein Centre for Minimally Invasive Surgery and Innovation, McGill University Health Centre, Montreal, Canada.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Lee
authors.forename: Pepa
authors.initials: P
authors.lastname: Kaneva
authors.forename: Eric
authors.initials: E
authors.lastname: Latimer
authors.forename: Liane S
authors.initials: LS
authors.lastname: Feldman
mesh_terms: D000328:Adult; D000368:Aged; D017081:Cholecystectomy, Laparoscopic / Q000523:psychology*; D005260:Female; D006304:Health Status; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D019057:Quality-Adjusted Life Years
keywords: GIQLI; SF-6D; Utility mapping; laparoscopic cholecystectomy; postoperative recovery