Abstract
Background and Purpose: A number of authors have calculated thresholds of individually minimally important individual change (MIC) for the Roland Morris Disability Questionnaire (RMDQ). However, at an individual level, the imprecision of the measurement instrument often exceeds the MIC. In recognition of this, there is some consensus on appropriate individual change thresholds (absolute and baseline-specific) for the RMDQ. These were intended to be re-evaluated as further data become available. With this in mind, we calculated the MIC and minimally detectable change (MDC) of the RMDQ in the UK BEAM population.
Method and Results: 1,334 patients enrolled in the UK BEAM trial completed the RMDQ. We calculated MIC using ROC curves from three and 12 month follow-up data, and using a seven-point health transition question as the external criterion. We performed sub-analyses of MIC for bands of baseline severity and considered adjusting these for regression to the mean (RTM). We calculated MDC based on within-person and residual error variances of stable patients’ repeated measurements. The overall MIC was four points and the MDC 7.6 points. These values fall around the centre of the ranges considered by the consensus study team. Higher MIC values were observed for more disabled patients; this may be partially an artefact of RTM. In our positively skewed population, more disabled patients required more than the consensus recommendation of 30% change from baseline.
Conclusion: This is further evidence that five RMDQ points is an appropriate threshold by which to judge individual change on the RMDQ. Proportional change from baseline may be more population-specific than previously thought.
Correspondence should be addressed to SBPR at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE, England.
