Open Access Open Badges Research article

Using the random forest method to detect a response shift in the quality of life of multiple sclerosis patients: a cohort study

Mohamed Boucekine1*, Anderson Loundou1, Karine Baumstarck1, Patricia Minaya-Flores1, Jean Pelletier2, Badih Ghattas3 and Pascal Auquier1

Author affiliations

1 EA3279, Self-perceived Health Assessment Research Unit, School of Medicine, Université de la Méditerranée, 27 bd Jean Moulin, Marseille cedex 05, F-13385, France

2 Departments of Neurology and CRMBM CNRS6612, Timone University Hospital, APHM, Marseille, France

3 Department of Mathematics, Faculté des Sciences de Luminy, Aix-Marseille University, Marseille, France

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Citation and License

BMC Medical Research Methodology 2013, 13:20  doi:10.1186/1471-2288-13-20

Published: 15 February 2013



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.


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.


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.


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.

Trial registration identifier: NCT00702065

Multiple sclerosis; Quality of life; Response shift; Random forest; MusiQoL; SF-36; Longitudinal studies; Variable importance