title: Introducing the Concept of the Minimally Important Difference to Determine a Clinically Relevant Change on Patient-Reported Outcome Measures in Patients with Intermittent Claudication.
abstract: OBJECTIVE
  The minimally important difference (MID) represents the smallest change in score on patient-reported outcome measures that is relevant to patients. The aim of this study was to introduce the MID for the Vascular Quality of Life Questionnaire (VascuQol) and the walking impairment questionnaire (WIQ) for patients with intermittent claudication (IC).
  
  
  METHODS
  In this multicenter study, we recruited 294 patients with IC between July and October 2012. Patients completed the VascuQol, with scores ranging from 1 to 7 (worst to best), and the WIQ, with scores ranging from 0 to 1 (worst to best) at first visit and after 4 months follow-up. In addition, patients answered an anchor-question rating their health status compared to baseline, as being improved, unchanged, or deteriorated. The MID for improvement and deterioration was calculated by an anchor-based approach, and determined with the upper and lower limits of the 95 % confidence interval of the mean change of the group who had not changed according to the anchor-question.
  
  
  RESULTS
  For the MID analyses of the VascuQol and WIQ, 163 and 134 patients were included, respectively. The MID values for the VascuQol (mean baseline score 4.25) were 0.87 for improvement and 0.23 for deterioration. For the WIQ (mean baseline score 0.39), we found MID values of 0.11 and -0.03 for improvement and deterioration, respectively.
  
  
  CONCLUSIONS
  In this study, we calculated the MID for the VascuQol and the WIQ. Applying these MID facilitates better interpretation of treatment outcomes and can help to set treatment goals for individual care.
authors.affiliation: Departments of Vascular Surgery and Interventional Radiology, Academic Medical Center, Meibergdreef 9, 1105, AZ, Amsterdam, The Netherlands. a.p.conijn@amc.nl.
authors.forename: Anne P
authors.initials: AP
authors.lastname: Conijn
authors.affiliation: Division of Health Care, Achmea Insurances, Burg. Roelenweg 13, 8021, EV, Zwolle, The Netherlands. wilma.jonkers@achmea.nl.
authors.forename: Wilma
authors.initials: W
authors.lastname: Jonkers
authors.affiliation: Department of Vascular Surgery, Erasmus Medical Center, 's-Gravendijkwal 230, 3015, CE, Rotterdam, The Netherlands. e.rouwet@erasmusmc.nl.
authors.forename: Ellen V
authors.initials: EV
authors.lastname: Rouwet
authors.affiliation: Department of Vascular Surgery, Onze Lieve Vrouwe Gasthuis, Oosterpark 9, 1091, AC, Amsterdam, The Netherlands. a.c.vahl@olvg.nl.
authors.forename: Anco C
authors.initials: AC
authors.lastname: Vahl
authors.affiliation: Department of Radiology, Academic Medical Center, Meibergdreef 9, 1105, AZ, Amsterdam, The Netherlands. j.a.reekers@amc.nl.
authors.forename: Jim A
authors.initials: JA
authors.lastname: Reekers
authors.affiliation: Department of vascular surgery, Academic Medical Center, Meibergdreef 9, 1105, AZ, Amsterdam, The Netherlands. m.j.koelemaij@amc.nl.
authors.forename: Mark J W
authors.initials: MJ
authors.lastname: Koelemay
mesh_terms: D000368:Aged; D017130:Angioplasty; D005081:Exercise Therapy; D005240:Feasibility Studies; D005260:Female; D005500:Follow-Up Studies; D006304:Health Status; D006801:Humans; D007383:Intermittent Claudication / Q000628:therapy*; D008297:Male; D009426:Netherlands; D063868:Patient Outcome Assessment; D010865:Pilot Projects; D011446:Prospective Studies; D011788:Quality of Life; D011795:Surveys and Questionnaires; D016896:Treatment Outcome; D016138:Walking
keywords: Biostatistics; Claudication; Clinical practice