The Minimal Important Difference in Physical Activity in Patients with COPD

PLoS One. 2016 Apr 28;11(4):e0154587. doi: 10.1371/journal.pone.0154587. eCollection 2016.


Background: 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.

Methods: 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.

Results: 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) 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.

Conclusions: The MID after pulmonary rehabilitation lies between 600 and 1100 The clinical importance of this change is supported by a reduced risk for hospital admission in those patients with more than 600 steps improvement.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Exercise / physiology*
  • Exercise Test
  • Exercise Tolerance / physiology*
  • Female
  • Hospitalization / statistics & numerical data
  • Humans
  • Male
  • Outcome Assessment, Health Care*
  • Pulmonary Disease, Chronic Obstructive / physiopathology*
  • Pulmonary Disease, Chronic Obstructive / rehabilitation*
  • Retrospective Studies
  • Surveys and Questionnaires

Grants and funding

This work was supported by the Flemish Research Foundation (grant # G.0871.13) and PROactive IMI-JU # 115011. DL and WJ are post-doctoral research fellows of the FWO-Flanders. CAC is supported by CNPq/Brazil (202425/2011-8). Ms Heleen Demeyer is the recipient of a joint ERS/SEPAR Fellowship (LTRF 2015).