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

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). CONCLUSION: RS was present and impacted HRQOL and utility assessment among patients undergoing total knee replacement before and 6 months after surgery.