How Can We Assess Outcomes of Clinical Trials: The MCID Approach

Figures & data

Table 1 Methods for estimating MCID

1.	Distribution (statistical) approach
	Estimate based on the distribution around the mean of the scores of the measure of interest in an untreated population
2.	Anchor (external measure) approach
	Compares scores of the measure of interest to other outcome measures, preferably those that have importance with more universal agreement and those with established MCID
3.	Opinion approach
	Gathers opinions of experts, patients, and health-care practitioners

Figure 1 A suggested taxonomy for changes in SGRQ score relative to the minimum clinically important difference (MCID). Lower score indicates better health. Error bars indicate 95% Confidence Intervals. Reproduced with permission from Jones PW. St. George's Respiratory Questionnaire: MCID. COPD 2005; 2:75–79.

Table 2 Suggested MCID of commonly used outcome measures in COPD²

Outcome Measure	Scale	Suggested MCID^b
Forced expiratory volume in 1 second	—	100 ml
Maximal exercise test	—	10 watts^c
Submaximal exercise endurance test	—	≥ 1.75 minutes
Six-minute walk test	—	37–71 meters
Transition Dyspnea Index	−9 to +9	1 unit
UCSD Shortness of Breath Questionnaire	0–120	5–7 units
Borg scale of perceived dyspnea	6–20	2 units
Visual analog scale of dyspnea	0–100	10–20
Breathlessness diary	0–4	0.20
St. George's Respiratory Questionnaire	0–100	4 units
Chronic Respiratory Disease Questionnaire	1–7	0.5 units
Quality of Well-Being Scale	0–1	0.03 units
Exacerbations	–	22% change;
		1 exacerbation/year
Fat-free mass or muscle mass	—	Not available

^aModified with permission from Make B, Casaburi R, Leidy NK. Interpreting Results from Clinical Trials: Understanding Minimal Clinically Important Differences in COPD Outcomes. COPD 2005, 2:1–5. These values are provided for informational purposes and should be considered estimates with tolerance levels, rather than definitive cut-off values. The development of ranges for these estimates is recommended.

^bSuggested MCID values are drawn from articles in Journal of COPD (COPD, 2005, volume 2, issue 1).

^cIn the context of lung volume reduction surgery as an intervention.