title: Using Patient-Reported Outcomes for Economic Evaluation: Getting the Timing Right.
abstract: BACKGROUND
  Patient-reported outcome measures (PROMs) are becoming increasingly popular in orthopedic surgery. Preoperative and postoperative follow-up often elicit PROMs in the form of generic quality-of-life instruments (e.g., Short Form health survey SF-12 [SF-12]) that can be used in economic evaluation to estimate quality-adjusted life-years (QALYs). However, the timing of postoperative measurement is still under debate.
  
  
  OBJECTIVE
  To explore the timing of postoperative PROMs collection and the implications for bias in QALY estimation for economic evaluation.
  
  
  METHODS
  We compared the accuracy of QALY estimation on the basis of utilities derived from the SF-12 at one of 6 weeks, 3 months, 6 months, and 12 months after total knee arthroplasty, under different methods of interpolation between points. Five years of follow-up data were extracted from the St. Vincent's Melbourne Arthroplasty Outcomes (SMART) registry (n = 484). The SMART registry collects follow-up PROMs annually and obtained more frequent outcomes on subset of patients (n = 133).
  
  
  RESULTS
  Postoperative PROM collection at 6 weeks, 6 months, or 12 months biased the estimation of QALY gain from total knee arthroplasty by -41% (95% confidence interval [CI] -59% to -22%), 18% (95% CI 4%-32%), and -8% (95% CI -18% to -2%), respectively. This bias was minimized by collecting PROMs at 3 months postoperatively (6% error; 95% CI -9% to 21%).
  
  
  CONCLUSIONS
  The timing of PROM collection and the interpolation assumptions between measurements can bias economic evaluation. In the case of total knee arthroplasty, we recommend a postoperative measurement at 3 months with linear interpolation between preoperative and postoperative measures. The design of economic evaluations should consider timing and interpolation issues.
authors.affiliation: Centre for Health Policy, School of Population and Global Health, the University of Melbourne, Carlton, Victoria, Australia; The University of Melbourne Department of Surgery, St. Vincent's Hospital, Fitzroy, Victoria, Australia. Electronic address: chris.schilling@unimelb.edu.au.
authors.forename: Chris
authors.initials: C
authors.lastname: Schilling
authors.affiliation: The University of Melbourne Department of Surgery, St. Vincent's Hospital, Fitzroy, Victoria, Australia; Department of Orthopaedics, St. Vincent's Hospital Melbourne, Melbourne, Victoria, Australia.
authors.forename: Michelle M
authors.initials: MM
authors.lastname: Dowsey
authors.affiliation: Centre for Health Policy, School of Population and Global Health, the University of Melbourne, Carlton, Victoria, Australia.
authors.forename: Philip M
authors.initials: PM
authors.lastname: Clarke
authors.affiliation: The University of Melbourne Department of Surgery, St. Vincent's Hospital, Fitzroy, Victoria, Australia; Department of Orthopaedics, St. Vincent's Hospital Melbourne, Melbourne, Victoria, Australia.
authors.forename: Peter F
authors.initials: PF
authors.lastname: Choong
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000191:economics*; D003362:Cost-Benefit Analysis; D005260:Female; D006801:Humans; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery*; D000071066:Patient Reported Outcome Measures; D011183:Postoperative Complications / Q000191:economics; D011788:Quality of Life; D019057:Quality-Adjusted Life Years; D013997:Time Factors
keywords: PROMs; economic evaluation; timing; total knee arthroplasty