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Deciding on progression of joint damage in paired films of individual patients: smallest detectable difference or change
  1. K Bruynesteyn1,
  2. M Boers2,
  3. P Kostense2,
  4. S van der Linden1,
  5. D van der Heijde1
  1. 1Department of Internal Medicine, Division of Rheumatology, University Hospital of Maastricht and CAPHRI Research Institute University of Maastricht, Maastricht, The Netherlands
  2. 2Department of Clinical Epidemiology and Biostatistics, VU University Medical Centre, Amsterdam, The Netherlands
  1. Correspondence to:
    Professor D van der Heijde
    Department of Internal Medicine, Division of Rheumatology, University Hospital Maastricht, PO Box 5800, 6202 AZ Maastricht, The Netherlands;


Progression of radiological joint damage is usually based on the simultaneous assessment of a series of films from an individual patient (“paired”, with or without known sequence). In this setting the degree of progression that can be reliably detected above the measurement error is best determined by the smallest detectable change, and overestimated by the traditionally calculated smallest detectable difference. This knowledge is important for calculation of the proportion of patients showing radiographic progression in clinical trials.

  • ANOVA, analysis of variance
  • SDC, smallest detectable change
  • SDD, smallest detectable difference
  • joint damage progression
  • rheumatoid arthritis

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