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The measurement of disease
  1. I S J Merkies1,2,3,
  2. R A C Hughes4
  1. 1Department of Neurology, University Medical Centre Maastricht, Maastricht, The Netherlands
  2. 2Department of Neurology, Erasmus Medical Centre, Rotterdam, The Netherlands
  3. 3Department of Neurology, Spaarne Hospital, Hoofddorp, The Netherlands
  4. 4Department of Neurology, MRC Centre for Neuromuscular Disease, Institute of Neurology, London, UK
  1. Correspondence to Professor Richard A C Hughes, Department of Neurology, MRC Centre for Neuromuscular Disease, Institute of Neurology, London WC1 3BG, UK; rhughes11{at}

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Lies, damn lies and statistics (Mark Twain) and thanks to Rasch analysis

In everyday clinical practice, we are forever asking patients whether they are the same, better or worse, and for everyday practice their answers and our memories often suffice. However, in chronic diseases such as neurology and rehabilitation including corresponding clinical trials, we need measures of the amount of change. Usually disability (activity limitation and participation restriction in modern terminology)1 is the most appropriate aspect of disease to measure because it is more meaningful for patients. It addresses the consequences of an underlying pathology and impairment deficits better than quality-of-life measures. Among the scales which have been developed for measuring disability are the 10-item Barthel index with altogether 30 response categories and the Functional Independence Measure motor scale with 13 items and 91 response categories. Both are widely used, and both have demonstrated their scientific soundness in various diseases with classical test theory-based …

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  • Competing interests ISJM and RACH have received honoraria for participation on the ICE Study Steering Committee.

  • Provenance and peer review Commissioned; not externally peer reviewed.

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