title: Toward the use of proxy reports for estimating long-term patient-reported outcomes in multiple sclerosis.
abstract: BACKGROUND
  Assessment of disease impact in multiple sclerosis (MS) is usually driven by information obtained directly from patients using patient-reported outcomes. However, when patients' response in longitudinal studies is less reliable or missing, proxy respondents may be used.
  
  
  OBJECTIVE
  The objective of this paper is to evaluate whether long-term patient scores can be reliably estimated using scores obtained from proxies.
  
  
  METHODS
  Baseline, six-month and two-year data were collected from 155 patients and proxies on the physical scale of the Multiple Sclerosis Impact Scale (MSIS-29). Linear regression analyses were performed with the patient two-year scores as outcome, proxy two-year scores as predictor and other variables that could contribute to a better prediction of the patient follow-up score.
  
  
  RESULTS
  The patient follow-up score could be predicted rather accurately (R(2) = 0.74) using the patient baseline score and the proxy follow-up score. The correlation between observed and predicted scores was 0.86. The model performed well in different follow-up durations and even better in an external cohort.
  
  
  CONCLUSIONS
  A simple model of a constant value (intercept), the patient baseline score and the proxy follow-up score can predict patients' follow-up score on the physical impact of MS.
authors.affiliation: VU University Medical Center, The Netherlands Judith.sonder@vumc.nl.
authors.forename: Judith M
authors.initials: JM
authors.lastname: Sonder
authors.affiliation: VU University Medical Center, The Netherlands.
authors.forename: Lisanne J
authors.initials: LJ
authors.lastname: Balk
authors.affiliation: VU University Medical Center, The Netherlands.
authors.forename: Femke A H
authors.initials: FA
authors.lastname: van der Linden
authors.affiliation: VU University Medical Center, The Netherlands.
authors.forename: Libertje V A E
authors.initials: LV
authors.lastname: Bosma
authors.affiliation: VU University Medical Center, The Netherlands.
authors.forename: Chris H
authors.initials: CH
authors.lastname: Polman
authors.affiliation: VU University Medical Center, The Netherlands.
authors.forename: Bernard M J
authors.initials: BM
authors.lastname: Uitdehaag
mesh_terms: D000328:Adult; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000175:diagnosis*; D017063:Outcome Assessment, Health Care / Q000379:methods* / Q000592:standards; D063868:Patient Outcome Assessment; D012720:Severity of Illness Index
keywords: MSIS; Multiple sclerosis; longitudinal research; outcome measurement; patient-reported outcome; proxy