Outcome Measures

Field Walking Tests

The data presented is from a wider systematic review of the minimum important difference of field walk tests further details can be found here:  https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=185565

Authors: E. Daynes 1,2, R.E. Barker 3,4, A. Jones 2, J.A. Walsh 3, C.M. Nolan 3,4, N.J. Greening 1,2, S. Singh 1,2, L. Houchen-Wolloff 1,2, R.A. Evans 1,2

  1. Centre of Exercise and Rehabilitation Sciences, National Institute of Health Research Biomedical Research Centre – Respiratory Theme, University Hospitals of Leicester NHS Trust, Leicester, UK.

  2. Department of Respiratory Sciences, University of Leicester, Leicester, UK.

  3. Harefield Respiratory Research Group, Royal Brompton and Harefield NHS Foundation Trust, UK

  4. National Heart and Lung Institute, Imperial College London, UK
    Summarised for the ATS PR Assembly website by L. Houchen-Wolloff 1,2, T Harvey-Dunstan 5 and R.A. Evans 1,2

  5. Division of Physiotherapy and Rehabilitation Sciences, School of Health Sciences, The University of Nottingham, Nottingham, UK.


Introduction: Field walking tests are commonly used to assess exercise performance in Chronic Respiratory Disease (CRD) such as the six-minute walk test [6MWT(1)], the incremental shuttle walk test [ISWT(2)] and the endurance shuttle walking test [ESWT(3)]. The aims of exercise testing are to assess the degree of functional limitation, to prescribe treatment and to measure the outcome of an intervention, for example, Pulmonary Rehabilitation (PR). It is important for clinicians and researchers to be able to interpret what constitutes a ‘meaningful change’ in exercise performance to infer whether a treatment has been successful and to inform sample size calculations for research studies (4). But what do we mean by a ‘meaningful change?’

In research trials, treatment effects are often reported as a change in the outcome measure supported by a measure of variability; for example, the mean change with 95% confidence intervals and a probability (p) value to indicate the level of statistical significance for normally distributed data. However, a statistically significant change may not indicate a clinically meaningful or important change for clinicians or patients to interpret. Minimum Important Differences can be calculated using an anchor-based approach (anchored to a global rating of change or another validated outcome measure) or distribution methods e.g. standard error of the measurement (SEM) (6). The anchor-based method typically derives a minimally clinical important difference (MCID) adding clinical relevance or patient experience to the reporting of an outcome measure. The MCID is defined as ‘the smallest difference in score in the outcome of interest that informed patients or informed proxies [who can be clinicians] perceive as important, either beneficial or harmful, and which would lead the patient or clinician to consider a change in the management’ (5).

There have been many studies that have developed an MID for either the ISWT and the 6MWT using a variety of methodologies and therefore it can be difficult for clinicians and researchers to determine which MID is appropriate. It is  important to understand the intervention used (Pulmonary Rehabilitation in this example), and population characteristics for the MID derivation as the MID is likely to be affected by disease severity, type of disease and symptoms. Where possible the MID for the intervention and particular population of interest should be used (7)

Studies evaluating a minimum important difference in walking distance to Pulmonary Rehabilitation in chronic respiratory disease

We have included 20 studies conducted in a range of chronic respiratory diseases (CRD’s) with three exercise tests ISWT (n=4), 6MWT (n=12) and ESWT (n=4).  The range of CRD’s identified included COPD (n=11; ISWT=2, 6MWT=5, ESWT=4), Non-cystic fibrosis (NCF) Bronchiectasis (n=2; ISWT=1, 6MWT=1), Interstitial Pulmonary Fibrosis (n=5; ISWT=1, 6MWT=4), Lung cancer (n=1 for the 6MWT), Respiratory Failure (n=1 for the 6MWT).  Findings for each MID can be seen below and in Table 1.  All but one study (10) applied a combined methodological approach employing both distribution and anchor based measures.


For patients with COPD (n=372 to 613) an MID of 35-47.5m is suggested by two studies (10, 11). For patients with Non-Cystic Fibrosis Bronchiectasis (n=37) a similar MID of 35m was suggested by one single study (12), and 31-46m has been proposed for patients with Interstitial Pulmonary Fibrosis (n=50 and 72) in a single study (13).


For patients with COPD/ severe COPD (n=75 to n=2112), an MID of 25-71m is suggested from five studies when including any proposed ranges (14-18).  When excluding any ranges (using absolute values), the suggested MID reduces to 25-54m.

A single study in patients with NCF-Bronchiectasis (n=37), identified an MCID of 25m (no ranges reported: 12).  As similar range has been proposed by four studies in patients with Interstitial Pulmonary Fibrosis (n=48 to 822) of 24-37m (19-22).

Only one study reported the MID as a marker for clinical deterioration for patients with lung cancer (n=56).  A deterioration of between 22-42m was considered clinically important (23).

A further study has reported an MID of 20-30m for patients diagnosed with acute respiratory failure [ARF (n=641)].  Underlying causes of ARF were not detailed in this paper (24).


COPD was the only CRD reporting an MID for the ESWT (n=55 to n=531).  Taking the four studies collectively, an MID of 144-279 seconds for time to limitation is proposed (25-28).  This included stated ranges for change.  One study was unable to accurately estimate an MID due to weak correlations between the anchors and the measured change in ESWT performance (27).


Summary: We have included 20 studies of MID for common exercise tests in CRD.  All but one study (10) applied a combined methodological approach employing both distribution and anchor based measures.


Exercise test Outcome Measure Condition Population Demographics Suggested MID (range) Assessment Method Author (n=)
Response to Pulmonary Rehabilitation or detecting clinical deterioration
ISWT Distance (m) COPD Age=69.4(8.4); Gender % Male=55%; FEV 1=1.06(0.53)L; FEV 1/FVC=50.8(18.1)%. 47.5mAdditional benefits identified at 78.7m. Anchor based Singh 2008 (n=372)Ref 10
Cohort 1: Age=68.8(9.3); Gender % Male=55.2%; FEV 1=1.06(0.51)L; FEV 1/FVC=44.2(12.3)%.

Cohort 2: Age=69.5(8.4); Gender % Male=56.5%; FEV1=0.95(0.0.43+D11)L; FEV1/FVC=45.1(11.1)%.
35-36.1m Anchor and distribution based Evans 2019 (=613)Ref 11
NCF-Bronchiectasis Age=63.0(13.0); Gender % Male=NR; FEV 1 % Predicted=76.9(18.3)%; FVC % Predicted=83.8(17.6)% 35m Anchor and distribution based Lee 2014 (n=37)Ref 12
IPF Study 1 : Age=75.0(7.0); Gender % Male=72%; FVC =2.17(0.68)L; FVC % Predicted=70.0(19.9)%.

Study 2: Age=74.0(7.0)); Gender % Male=69%; FVC =2.30(0.70)L; FVC % Predicted=76.7(19.8)%.
31-46m Anchor and distribution based Nolan 2017 (Study 1 n=50; Study 2 n=72)Ref 13
6MWT Distance (m) COPD Age=70.3(8.5); Gender % Male=58.6%; FEV 1=1.26(0.55); FEV 1/FVC=49.0(16.0)%. 25m (no range reported) Anchor and distribution based Holland 2010 (n=75)Ref 14
Age=63.4(7.1); Gender % Male=65.0%; FEV 1% Pred=48.4(15.7)%. - 30m Anchor based approach in the context of worsening clinical status Polkey 2013 (n=2112)Ref 15
Age=67.0(10.0); Gender % Male=53.0%; FEV 1=0.98(0.45). 54 (37-71)m Anchor and distribution based Redelmeier 1997 (n=112)Ref 16
Age=68.9(8.3); Gender % Male=71.0%; FEV 1 % Predicted=39.2(14.1)%. 35 (30-42)m Systematic review of 9 studies Anchor and distribution based Puhan 2008 (n=460)Ref 17
Severe COPD Age=66.4(6.1); Gender % Male=61.2%; FEV 1 % Predicted=26.9(7.1). 26 (24-28)m Anchor and distribution based Puhan 2011 (n=1218)Ref 18
NCF-Bronchiectasis Age=63.0(13.0); Gender % Male=NR; FEV 1 % Predicted=76.9(18.3)%; FVC % Predicted=83.8(17.6)% 25m Anchor and distribution based Lee 2014 (n=37)Ref 12
Idiopathic Pulmonary Fibrosis Age=65.1(8.7); Gender % Male=73%; FVC =2.60(0.71)L; FVC % Predicted=67.8(11.8)%. 28m Anchor and distribution based Swigris 2010 (n=123)Ref 19
Age=69.0(9.0); Gender % Male=NR; FVC % Predicted=78.0(16.0)%. 29-34m Anchor and distribution based Holland 2009 (n=48)Ref 20
Age=66.0(7.8); Gender % Male=71%; FVC % Predicted=72.5(12.7)%. 24-45m Anchor and distribution based Du Bois 2011 (822)Ref 21
Age=66.5(5.6); Gender % Male=73%; FVC % Predicted=74.7(14.9)%. 21.7-37m Anchor and distribution based Nathan 2015 (n=338)Ref 22
Lung Cancer Age=65.0(10.0); Gender % Male=61%. - 22-42m Anchor and distribution based in the clinical context of deterioration. Granger 2015 (n=56)Ref 23
Acute Respiratory Failuresurvival Study 1*: Age=48.0(14.0); Gender % Male=57%; Lung function=NR.

Study 2**: Age=48.0(15.0); Gender % Male=61%; Lung function=NR.

Study 3~: Age=57.0(16.0); Gender % Male=72%; Lung function=NR.

Study 4 #: Age=59.0(15.0); Gender % Male=60%; Lung function=NR.
113m (94-132)m Anchor and distribution based Chan 2015 (n=641;  *162; **183; ~180; #126)Ref 24
ESWT Time (sec) COPD Age=62.0(9.0); Gender % Male=58%; FEV 1=0.84(0.34); FEV 1/FVC=31.8(9.2)%. 144 (186-199)sec Anchor and distribution based Altenburg  2015 (n=55)Ref 25
Age=70.0(8.0); Gender % Male=NR; FEV 1=1.11(0.40); FEV 1/FVC=43.0(13.0)%. 227 (70-156)sec Anchor and distribution based Hill 2019 (n=78)
Age=68.0(11.0); Gender % Male=57%; FEV 1=1.19(0.56); FEV 1/FVC=50.0(17.0)%. Unable to estimate Anchor and distribution based Pepin 2011 (n=132)
Age=69.4(9.1); Gender % Male=57%; FEV 1=1.29(0.58); FEV 1/FVC=51.2(16.4)%. 174-279sec Anchor and distribution based Zatloukal 2019 (n=531)
MD= mean; (SD)=standard deviation; Med=Median; [IQR]=Interquartile range; n=number of subjects; m=metre; NR=not reported; FEV 1=forced expiratory volume in one second; FVC=forced vital capacity; L=litre; Sec=second;


Reference List

  1. Butland RJ, Pang J, Gross ER, et al. Two-, six-, and 12-minute walking tests in respiratory disease. Br Med J (Clin Res Ed) 1982; 284(6329): 1607–1608.
  2. Singh SJ, Morgan MD, Scott S, et al. Development of a shuttle walking test of disability in patients with chronic airways obstruction. Thorax 1992; 47(12): 1019–1024.
  3. Revill SM, Morgan MD, Singh SJ, Williams J, Hardman AE. The endurance shuttle walk: a new field test for the assessment of endurance capacity in chronic obstructive pulmonary disease. Thorax 1999 Mar;54(3):213-22.
  4. Schunemann HJ and Guyatt GH. Commentary – goodbye M(C)ID! Hello MID, where do you come from? Health Serv Res 2005; 40(2): 593–597.
  5. Copay AG, Subach BR, Glassman SD, Polly DW, Jr., Schuler TC. Understanding the minimum clinically important difference: a review of concepts and methods. Spine J 2007 Sep;7(5):541-6.
  6. Brozek JL, Guyatt GH, Schunemann HJ. How a well-grounded minimal important difference can enhance transparency of labelling claims and improve interpretation of a patient reported outcome measure. Health Qual Life Outcomes 2006 Sep 27;4:69.
  7. Houchen-Wolloff L and Evans RA. Unravelling the mystery of the ‘Minimum Important Difference’ using practical outcome measures in chronic respiratory disease. Chronic Respiratory Disease. January 2019. 16:1479973118816491. doi: 10.1177/1479973118816491.
  8. Moher D, Liberati A, Tetzlaff J, Altman DG, The PRISMA Group (2009). Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement. PLoS Med 6(7): e1000097. doi:10.1371/journal.pmed1000097.
  9. Mokkink LB, de Vet HCW, Prinsen CAC, Patrick DL, Alonso J, Bouter LM, et al. COSMIN Risk of Bias checklist for systematic reviews of Patient-Reported Outcome Measures. Qual Life Res 2018 May;27(5):1171-9.
  10. Singh SJ, Jones PW, Evans R, Morgan MD. Minimum clinically important improvement for the incremental shuttle walking test. Thorax 2008 Sep;63(9):775-7.
  11. Evans RA, Singh SJ. Minimum important difference of the incremental shuttle walk test distance in patients with COPD. Thorax. 2019 Oct;74(10):994-995.
  12. Lee AL, Hill CJ, Cecins N, Jenkins S, McDonald CF, Burge AT, et al. Minimal important difference in field walking tests in non-cystic fibrosis bronchiectasis following exercise training. Respir Med 2014 Sep;108(9):1303-9.
  13. Nolan CM, Delogu V, Maddocks M, Patel S, Barker RE, Jones SE, Kon SSC, Maher TM, Cullinan P, Man WD. Validity, responsiveness and minimum clinically important difference of the incremental shuttle walk in idiopathic pulmonary fibrosis: a prospective study. Thorax. 2017 Sep 7:thoraxjnl-2017-210589. doi: 10.1136/thoraxjnl-2017-210589.
  14. Holland AE, Hill CJ, Rasekaba T, Lee A, Naughton MT, McDonald CF. Updating the minimal important difference for six-minute walk distance in patients with chronic obstructive pulmonary disease. Arch Phys Med Rehabil 2010 Feb;91(2):221-5.
  15. Polkey MI, Spruit MA, Edwards LD, Watkins ML, Pinto-Plata V, Vestbo J, et al. Six-minute-walk test in chronic obstructive pulmonary disease: minimal clinically important difference for death or hospitalization. Am J Respir Crit Care Med 2013 Feb 15;187(4):382-6.
  16. Redelmeier DA, Bayoumi AM, Goldstein RS, Guyatt GH. Interpreting small differences in functional status: the Six Minute Walk test in chronic lung disease patients. Am J Respir Crit Care Med 1997 Apr;155(4):1278-82.
  17. Puhan MA, Mador MJ, Held U, Goldstein R, Guyatt GH, Schünemann HJ. Interpretation of treatment changes in 6-minute walk distance in patients with COPD. Eur Respir J. 2008 Sep;32(3):637-43.
  18. Puhan MA, Chandra D, Mosenifar Z, Ries A, Make B, Hansel NN, et al. The minimal important difference of exercise tests in severe COPD. Eur Respir J 2011 Apr;37(4):784-90.
  19. Swigris JJ, Wamboldt FS, Behr J, du Bois RM, King TE, Raghu G, et al. The 6 minute walk in idiopathic pulmonary fibrosis: longitudinal changes and minimum important difference. Thorax 2010 Feb;65(2):173-7.
  20. Holland AE, Hill CJ, Conron M, Munro P, McDonald CF. Small changes in six-minute walk distance are important in diffuse parenchymal lung disease. Respir Med 2009 Oct;103(10):1430-5.
  21. du Bois RM, Weycker D, Albera C, Bradford WZ, Costabel U, Kartashov A, et al. Six-minute-walk test in idiopathic pulmonary fibrosis: test validation and minimal clinically important difference. Am J Respir Crit Care Med 2011 May 1;183(9):1231-7.
  22. Nathan SD, du Bois RM, Albera C, Bradford WZ, Costabel U, Kartashov A, Noble PW, Sahn SA, Valeyre D, Weycker D, King TE Jr. Validation of test performance characteristics and minimal clinically important difference of the 6-minute walk test in patients with idiopathic pulmonary fibrosis. Respir Med. 2015 Jul;109(7):914-22.
  23. Granger CL, Holland AE, Gordon IR, Denehy L. Minimal important difference of the 6-minute walk distance in lung cancer. Chron Respir Dis. 2015 May;12(2):146-54.
  24. Chan KS, Pfoh ER, Denehy L, Elliott D, Holland AE, Dinglas VD, Needham DM. Construct validity and minimal important difference of 6-minute walk distance in survivors of acute respiratory failure. Chest. 2015 May;147(5):1316-1326.
  25. Altenburg WA, Duiverman ML, Ten Hacken NH, Kerstjens HA, de Greef MH, Wijkstra PJ, et al. Changes in the endurance shuttle walk test in COPD patients with chronic respiratory failure after pulmonary rehabilitation: the minimal important difference obtained with anchor- and distribution-based method. Respir Res 2015 Feb 19;16:27.
  26. Hill K, Ng C, Wootton SL, McKeough ZJ, Eastwood PR, Hillman DR, Jenkins C, Spencer L, Jenkins SC, Cecins NM, Alison JA. The minimal detectable difference for endurance shuttle walk test performance in people with COPD on completion of a program of high-intensity ground-based walking. Respir Med. 2019 Jan;146:18-22. doi: 10.1016/j.rmed.2018.11.013.
  27. Pepin V, Laviolette L, Brouillard C, Sewell L, Singh SJ, Revill SM, et al. Significance of changes in endurance shuttle walking performance. Thorax 2011 Feb;66(2):115-20.
  28. Zatloukal J, Ward S, Houchen-Wolloff L, Harvey-Dunstan T, Singh S. The minimal important difference for the endurance shuttle walk test in individuals with chronic obstructive pulmonary disease following a course of pulmonary rehabilitation. Chronic Respiratory Disease. January 2019. doi:10.1177/1479973119853828