Table 6– Minimal important difference (MID) estimates for 6-min walking distance in patients with chronic respiratory disease
First author [ref.]Patient populationStudy designInterventionMID estimationProposed MID
Anchor-basedDistribution-basedOther method
Redelmeier [83]Moderate to severe COPDProspective, single armRehabilitationNANABetween-patient ratings: 54 m54 m
Wise [192]Severe to very severe COPDProspective, single arm within RCTNone (test–retest)NASEM: 45.3 m;
ES: 47.0 m;
CRM: 80.0 m;
average across three estimates: 57.4 m
NANo specific estimates (range 45–80 m)
Puhan [193]Moderate to severe COPDProspective, single armRehabilitationNASEM: 35 (30–42) m;
ERES: 42 m;
average across three estimates: 35.3 m
NA35 m (triangulation)
Holland [84]Moderate to severe COPDProspective, single armRehabilitation25 (20–61) mSRM: 1.2;
SEM: 25.5 m;
average across two estimates: 26.0 m
NA25 m (triangulation)
Puhan [194]Severe to very severe COPDRCTLVRS or medical treatment18.9 (18.1–20.1) m;
24.2 (23.4–25.4) m;
24.6 (23.4–25.7) m;
26.4 (25.4–27.4) m;
average across four estimates: 23.5 m
ES: 26.8 m;
SEM: 30.6 m;
ERES: 25.7 m;
average across three estimates: 27.7 m
NA26 m (triangulation)
Polkey [195]Mild to very severeProspective, observationalNone30 mNANA30 m
Holland [85]Moderate to severe DPLD (50% IPF)Prospective, single armRehabilitation30.5 mSEM: 33 mNA30–33 m
Swigris [196]Moderate to severe IPFRCTBosentan21.6 m41.3 mNA28 m (mean of all MIDs)
du Bois [62]Moderate to severe IPFRCTInterferon-γ-1b24 mSEM: 45 mNANo specific estimates (range 24–45 m)
Gilbert [197]Moderate to severe PAHRCTSildenafil (three different dosages)NAES: 31.2 m;
SEM: 24.7 m;
Sdiff: 37.8;
average across three estimates: 31.2 m
NA41 m (median across all estimates)
Mathai [198]Moderate to severe PAHRCTTadalafil or placebo38.6 mES: 38.5 m;
SRM: 0.2;
SEM: 25.1 m;
average across three estimates: 30.8 m
NA33 m (triangulation)
  • Data are presented as value (95% CI), unless otherwise stated. COPD: chronic obstructive pulmonary disease; NA: not available; RCT: randomised controlled trial; SEM: standard error of the measurement; ES: effect size (0.5×baseline sd); CRM: coefficient of repeated measurements; ERES: empirical rule effect size; SRM: standardised response mean (mean change/sd of change); LVRS: lung volume reduction surgery; DPLD: diffuse parenchymal lung disease; IPF: idiopathic pulmonary fibrosis; PAH: pulmonary arterial hypertension; Sdiff: standard error of the difference, a measure of errors associated with longitudinal change in a measure, Sdiff=√((SEM at baseline)2+(SEM at end of treatment)2).