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Proposal of a linear definition of the Bath Ankylosing Spondylitis Metrology Index (BASMI) and comparison with the 2-step and 10-step definitions
  1. Désirée van der Heijde (d.vanderheijde{at}kpnplanet.nl)
  1. Leiden University Medical Center, Netherlands
    1. Robert Landewé (rlan{at}sint.azm.nl)
    1. University of Maastricht, Netherlands
      1. Ernst Feldtkeller (e.feldtkeller{at}t-online.de)
      1. Ankylosing Spondylitis International Federation, Germany

        Abstract

        Background: The Bath Ankylosing Spondylitis Metrology Index (BASMI), characterizes the spinal mobility of patients with ankylosing spondylitis. Two versions have been published using categorical scores with either scores 0-2 for each of the five assessments, or scores 0–10. For metric purposes, we recently defined a BASMI version with linear score definitions.

        Aim: to evaluate agreement between three BASMI definitions and to test sensitivity-to-change.

        Patients and methods: The performance of the BASMI2 (based on the 2-step function), BASMI10 (based on the 10-step function), and BASMIlin (based on the linear function), are compared in 598 status assessments and 222 follow-up assessments with a 24 week interval after an intervention with either placebo or a TNF-blocker from various cohorts of patients with AS. Descriptive statistics and Bland & Altman plots were applied to compare the pair wise agreement of the three definitions. To assess sensitivity to change, Guyatt’s effect size using change data from the placebo and actively treated patients were used.

        Results: Bland & Altman analysis showed that the differences between BASMI2 scores and scores obtained by either of the two other definitions were highly dependent on the magnitude of the measurement. Guyatt’s effect sizes were 0.66 for the BASMI2, 0.95 for the BASMI10, and 1.04 for the BASMIlin, respectively, demonstrating best sensitivity to change for the newly developed BASMIlin.

        Conclusions: The BAMSI10 and BASMIlin have clear metric advantages as compared to BASMI2 among which its feasibility in computer evaluations and superior sensitivity to change. The BASMI10 and BASMI2 are not interchangeable.

        • Bath Ankylosing Spondylitis Metrology Index
        • ankylosing spondylitis
        • outcome assessment
        • spinal mobility
        • validation

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