title: The Minimal Important Difference in Physical Activity in Patients with COPD.
abstract: Changes in physical activity (PA) are difficult to interpret because no framework of minimal important difference (MID) exists. We aimed to determine the minimal important difference (MID) in physical activity (PA) in patients with Chronic Obstructive Pulmonary Disease and to clinically validate this MID by evaluating its impact on time to first COPD-related hospitalization.
  
  
  
  PA was objectively measured for one week in 74 patients before and after three months of rehabilitation (rehabilitation sample). In addition the intraclass correlation coefficient was measured in 30 patients (test-retest sample), by measuring PA for two consecutive weeks. Daily number of steps was chosen as outcome measurement. Different distribution and anchor based methods were chosen to calculate the MID. Time to first hospitalization due to an exacerbation was compared between patients exceeding the MID and those who did not.
  
  
  
  Calculation of the MID resulted in 599 (Standard Error of Measurement), 1029 (empirical rule effect size), 1072 (Cohen's effect size) and 1131 (0.5SD) steps.day-1. An anchor based estimation could not be obtained because of the lack of a sufficiently related anchor. The time to the first hospital admission was significantly different between patients exceeding the MID and patients who did not, using the Standard Error of Measurement as cutoff.
  
  
  
  The MID after pulmonary rehabilitation lies between 600 and 1100 steps.day-1. The clinical importance of this change is supported by a reduced risk for hospital admission in those patients with more than 600 steps improvement.
authors.affiliation: KU Leuven-University of Leuven, Department of Rehabilitation Sciences, B-3000 Leuven, Belgium.|University Hospitals Leuven, Department of Respiratory Diseases, B-3000 Leuven, Belgium.|Center for research in environmental epidemiology (CREAL), Barcelona, Spain.
authors.forename: Heleen
authors.initials: H
authors.lastname: Demeyer
authors.affiliation: KU Leuven-University of Leuven, Department of Rehabilitation Sciences, B-3000 Leuven, Belgium.|Rehabilitation Research Centre, Biomedical Research Institute, Faculty of Medicine and Life Sciences, Hasselt University, Diepenbeek, Belgium.
authors.forename: Chris
authors.initials: C
authors.lastname: Burtin
authors.affiliation: KU Leuven-University of Leuven, Department of Rehabilitation Sciences, B-3000 Leuven, Belgium.|University Hospitals Leuven, Department of Cardiovascular Sciences, B-3000 Leuven, Belgium.
authors.forename: Miek
authors.initials: M
authors.lastname: Hornikx
authors.affiliation: KU Leuven-University of Leuven, Department of Rehabilitation Sciences, B-3000 Leuven, Belgium.|University Hospitals Leuven, Department of Respiratory Diseases, B-3000 Leuven, Belgium.
authors.forename: Carlos Augusto
authors.initials: CA
authors.lastname: Camillo
authors.affiliation: KU Leuven-University of Leuven, Department of Rehabilitation Sciences, B-3000 Leuven, Belgium.|University Hospitals Leuven, Department of Respiratory Diseases, B-3000 Leuven, Belgium.|Red Cross Flanders, Centre for Evidence-Based Practice, Mechelen, Belgium.
authors.forename: Hans
authors.initials: H
authors.lastname: Van Remoortel
authors.affiliation: KU Leuven-University of Leuven, Department of Rehabilitation Sciences, B-3000 Leuven, Belgium.|University Hospitals Leuven, Department of Respiratory Diseases, B-3000 Leuven, Belgium.
authors.forename: Daniel
authors.initials: D
authors.lastname: Langer
authors.affiliation: University Hospitals Leuven, Department of Respiratory Diseases, B-3000 Leuven, Belgium.
authors.forename: Wim
authors.initials: W
authors.lastname: Janssens
authors.affiliation: KU Leuven-University of Leuven, Department of Rehabilitation Sciences, B-3000 Leuven, Belgium.|University Hospitals Leuven, Department of Respiratory Diseases, B-3000 Leuven, Belgium.
authors.forename: Thierry
authors.initials: T
authors.lastname: Troosters
mesh_terms: D000368:Aged; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D017063:Outcome Assessment, Health Care; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology* / Q000534:rehabilitation*; D012189:Retrospective Studies; D011795:Surveys and Questionnaires