title: Minimally important change determined by a visual method integrating an anchor-based and a distribution-based approach.
abstract: BACKGROUND
  Minimally important changes (MIC) in scores help interpret results from health status instruments. Various distribution-based and anchor-based approaches have been proposed to assess MIC.
  
  
  OBJECTIVE
  To describe and apply a visual method, called the anchor-based MIC distribution method, which integrates both approaches.
  
  
  METHODS
  Using an anchor, patients are categorized as persons with an important improvement, an important deterioration, or without important change. For these three groups the distribution of the change scores on the health status instrument are depicted in a graph. We present two cut-off points for an MIC: the ROC cut-off point and the 95% limit cut-off point.
  
  
  RESULTS
  We illustrate our anchor-based MIC distribution method determining the MIC for the Pain Intensity Numerical Rating Scale in patients with low back pain, using two conceivable definitions of minimal important change on the anchor. The graph shows the distribution of the scores of the health status instrument for the relevant categories on the anchor, and also the consequences of choosing the ROC cut-off point or the 95% limit cut-off point.
  
  
  CONCLUSIONS
  The anchor-based MIC distribution method provides a general framework, applicable to all kind of anchors. This method forces researchers to choose and justify their choice of an appropriate anchor and to define minimal importance on that anchor. The MIC is not an invariable characteristic of a measurement instrument, but may depend, among other things, on the perspective from which minimal importance is considered and the baseline values on the measurement instrument under study. A balance needs to be struck between the practicality of a single MIC value and the validity of a range of MIC values.
authors.affiliation: EMGO Institute, VU University Medical Center, Amsterdam, The Netherlands. hcw.devet@vuc.nl
authors.forename: Henrica C W
authors.initials: HC
authors.lastname: de Vet
authors.forename: Raymond W J G
authors.initials: RW
authors.lastname: Ostelo
authors.forename: Caroline B
authors.initials: CB
authors.lastname: Terwee
authors.forename: Nicole
authors.initials: N
authors.lastname: van der Roer
authors.forename: Dirk L
authors.initials: DL
authors.lastname: Knol
authors.forename: Heleen
authors.initials: H
authors.lastname: Beckerman
authors.forename: Maarten
authors.initials: M
authors.lastname: Boers
authors.forename: Lex M
authors.initials: LM
authors.lastname: Bouter
mesh_terms: D006305:Health Status Indicators; D006801:Humans; D017116:Low Back Pain / Q000175:diagnosis*; D010147:Pain Measurement / Q000592:standards*; D011788:Quality of Life; D012372:ROC Curve; D011795:Surveys and Questionnaires / Q000592:standards*