title: An exploratory study of response shift in health-related quality of life and utility assessment among patients with osteoarthritis undergoing total knee replacement surgery in a tertiary hospital in Singapore.
abstract: OBJECTIVE
  To investigate the influence of response shift (RS) on health-related quality of life (HRQOL) and utility assessment among patients undergoing total knee replacement.
  
  
  METHODS
  Consenting patients undergoing total knee replacement were interviewed to determine their HRQOL by using the six-dimensional health state short form, derived from SF-36, and the EuroQol five-dimensional questionnaire at baseline (pretest 1) and the six-dimensional health state short form, derived from SF-36, at 6 (pretest 2) and 18 months after surgery (post-test). RS was studied by using a "then-test" approach by contacting participants 18 months after surgery and asking them to evaluate their HRQOL at baseline (then-test 1) and at 6 (then-test 2) and 18 months after surgery. RS was calculated as the score difference between pretest and then-test scores for a given time point. Relationships between RS and external variables were explored by using univariate and multiple liner regression analyses.
  
  
  RESULTS
  In 74 subjects (63% response rate, median age 68 years), median (interquantile range) six-dimensional health state short form, derived from SF-36, scores for then-tests at baseline (0.48 [0.42-0.49]) and at 6 months (0.72 [0.66-0.79]) after surgery were significantly different from respective pretest scores (0.61 [0.58-0.68] at baseline, P = 0.000; 0.69 [0.63-0.72] at 6 months, P = 0.000), showing RS at both time points. RS at baseline (0.14 [0.08-0.20]) was significantly larger than that at 6 months (-0.05 [0.14 to 0.00], P = 0.000). EuroQol five-dimensional questionnaire pretest and then-test scores at baseline also differed significantly (0.69 [0.17-0.73] vs. -0.18 [-0.23 to 0.00], P = 0.000). RS at baseline was not affected by assessed demographic or medical variables. RS at 6 months was greater in subjects with more years of education (16% of variance in multiple liner regression, P < 0.01).
  
  
  CONCLUSIONS
  RS was present and impacted HRQOL and utility assessment among patients undergoing total knee replacement before and 6 months after surgery.
authors.affiliation: Department of Pharmacy, National University of Singapore, Singapore.
authors.forename: Xu-Hao
authors.initials: XH
authors.lastname: Zhang
authors.forename: Shu-Chuen
authors.initials: SC
authors.lastname: Li
authors.forename: Feng
authors.initials: F
authors.lastname: Xie
authors.forename: Ngai-Nung
authors.initials: NN
authors.lastname: Lo
authors.forename: Kwang-Ying
authors.initials: KY
authors.lastname: Yang
authors.forename: Seng-Jin
authors.initials: SJ
authors.lastname: Yeo
authors.forename: Kok-Yong
authors.initials: KY
authors.lastname: Fong
authors.forename: Julian
authors.initials: J
authors.lastname: Thumboo
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery*; D011788:Quality of Life; D012846:Singapore