title: Using the random forest method to detect a response shift in the quality of life of multiple sclerosis patients: a cohort study.
abstract: BACKGROUND
  Multiple sclerosis (MS), a common neurodegenerative disease, has well-described associations with quality of life (QoL) impairment. QoL changes found in longitudinal studies are difficult to interpret due to the potential response shift (RS) corresponding to respondents' changing standards, values, and conceptualization of QoL. This study proposes to test the capacity of Random Forest (RF) for detecting RS reprioritization as the relative importance of QoL domains' changes over time.
  
  
  METHODS
  This was a longitudinal observational study. The main inclusion criteria were patients 18 years old or more with relapsing-remitting multiple sclerosis. Every 6 months up to month 24, QoL was recorded using generic and MS-specific questionnaires (MusiQoL and SF-36). At 24 months, individuals were divided into two 'disability change' groups: worsened and not-worsened patients. The RF method was performed based on Breiman's description. Analyses were performed to determine which QoL scores of SF-36 predicted the MusiQoL index. The average variable importance (AVI) was estimated.
  
  
  RESULTS
  A total of 417 (79.6%) patients were defined as not-worsened and 107 (20.4%) as worsened. A clear RS was identified in worsened patients. While the mental score AVI was almost one third higher than the physical score AVI at 12 months, it was 1.5 times lower at 24 months.
  
  
  CONCLUSIONS
  This work confirms that the RF method offers a useful statistical approach for RS detection. How to integrate the RS in the interpretation of QoL scores remains a challenge for future research.
  
  
  BACKGROUND
  ClinicalTrials.gov identifier: NCT00702065.
authors: EA3279, Self-perceived Health Assessment Research Unit, School of Medicine, Université de la Méditerranée, Marseille cedex 05, France. boucekine.m@gmail.com
authors: Mohamed
authors: M
authors: Boucekine
authors: Anderson
authors: A
authors: Loundou
authors: Karine
authors: K
authors: Baumstarck
authors: Patricia
authors: P
authors: Minaya-Flores
authors: Jean
authors: J
authors: Pelletier
authors: Badih
authors: B
authors: Ghattas
authors: Pascal
authors: P
authors: Auquier
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008016:Life Change Events; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000175:diagnosis / Q000503:physiopathology / Q000523:psychology*; D011788:Quality of Life; D012044:Regression Analysis; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires