Deconstructing the Minimum Clinically Important Difference (MCID)

Figures & data

Table 1 Anchor Questions

Outcome Domain	Measurement Source	Anchor Question
KOOS Pain	VR12	“During the past 4 weeks, how much did pain interfere with your normal work (including both work outside the home and housework)?”
	PROMIS	“How would you rate your pain on average?”
VR12 PCS	KOOS ADL	“The following question concerns your physical function. By this we mean your ability to move around and to look after yourself. For the following activity please indicate the degree of difficulty you have experienced in the last week due to your surgical knee. If you are not able to do the activity listed, tell us how difficult it would be if you attempted to do the activity. ‘Rising from sitting’”
	PROMIS	“To what extent are you able to carry out your everyday physical activities such as walking, climbing stairs, carrying groceries, or moving a chair?”

Note: Bold text indications assessment domain.

Figure 1 ROC curves for KOOS pain subscale demonstrating the effects of the anchor question upon both magnitude and precision of the MCID. (A) Anchor question derived from the VR-12. (B) Anchor question derived from PROMIS. The statistical significance (p value) applies to the measure of precision (C-index).

Figure 2 ROC curves for PCS function domain demonstrating the effects of the threshold criteria from a Likert scale upon both magnitude and precision of the MCID. (A) Success criteria 3–5. (B) Success criteria 4–5. The statistical significance (p value) applies to the measure of precision (C-index).

Table 2 Estimated MCID for KOOS Pain

	MCID	C-Index	P-value
Varying Anchor Questions			<0.0001
VR-12 Anchor	15.99	0.68
PROMIS Anchor	31.26	0.77
Varying Criteria for Success/Failure			<0.0001
Criteria 1 (0–3 Clinical Success)	31.26	0.77
Criteria 2 (0–6 Clinical Success)	6.26	0.56
Varying Sample Size			<0.0001
Sample Size of 50	25.06	0.53
Sample Size of 100	31.26	0.77

Table 3 Estimated MCID for PCS

	MCID	C-index	P-value
Varying Anchor Questions			<0.0001
VR-12 Anchor	6.67	0.50
PROMIS Anchor	1.03	0.77
Varying Criteria for Success/Failure			<0.0001
Criteria 1 (3–5 Clinical Success)	1.03	0.75
Criteria 2 (4–5 Clinical Success)	2.46	0.58
Varying Sample Size			<0.0001
Sample Size of 50	12.19	0.50
Sample Size of 100	2.46	0.53